Electronic device having pixels displaying an image and pixels displaying an operation key

ABSTRACT

An easy to use electronic device is provided. The electronic device functions as a telephone and has a display portion, an audio input portion, an audio output portion, and operation keys. The display portion has a passive element, and the operation keys have LEDs. The direction of an image displayed by the LEDs is switchable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/465,567, filed Aug. 18, 2006 now U.S. Pat. No. 7,489,777, nowallowed, which is a continuation of U.S. application Ser. No.09/811,837, filed Mar. 20, 2001, now U.S. Pat. No. 7,194,085, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 2000-080973 on Mar. 22, 2000, all of which are incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device functioning as atelephone machine (telephone), and particularly to a portableinformation terminal. The present invention relates in particular to aportable information terminal having EL elements in a display portion.Note that, is in this specification, a portable information terminaldenotes a communication device capable of being carried by a user andwhich possesses both a function of being able to exchange data withanother individual while in motion, and a function as a telephone.

2. Description of the Related Art

Technology relating to flat panel displays has been developing rapidlyin recent years under the background of increasing needs for lighter,thinner, and smaller displays. Flat panel displays are capable ofdisplaying an image which is high quality, full color, and has highresolution. One type of flat panel display, liquid crystal displaydevices, are used in display portions of portable information terminals(such as a mobile computer, a portable telephone, a portable type gamemachine, and an electronic book).

FIG. 25 shows a portable telephone, which is one type of portableinformation terminal having a liquid crystal display device. Theportable telephone shown in FIG. 25 includes a main body 2801, an audiooutput portion 2802, an audio input portion 2803, a display portion2804, operation keys 2805, and an antenna 2806.

The portable telephone shown in FIG. 25 has a function as a telephone,namely it converts audio input to the audio input portion 2803 intoelectric waves and then outputs the electric waves, and it takes inelectric waves having audio information to convert it to audio, thenplays the audio in the audio output portion.

A liquid crystal display device is used in the display portion 2804, andis capable of displaying necessary information.

With the conventional portable information terminal shown in FIG. 25,images such as characters, numerals, or symbols are listed on ordisplayed on the operation keys so that the operator can recognize whattype of information is input to the portable information terminal whenwhich operation key is pressed. However, the direction of thecharacters, numerals, or symbols displayed on the operation keys isalways fixed with a conventional portable information terminal. Theoperator therefore must use the portable information terminal by alwaysaligning with the direction of the characters, numerals, or symbolsdisplayed on the operation key, and the portable information terminalitself is not user friendly.

SUMMARY OF THE INVENTION

In view of the above problem, an object of the present invention is toprovide a portable information terminal which is easy to use.

A portable information terminal of the present invention has operationkeys for inputting information, each with an LED (light emitting diode),EL display device, or liquid crystal display device, and by displayingcharacters, symbols, and numerals in the operation keys in accordancewith the LEDs, EL display devices, or liquid crystal display devices, anoperator can differentiate between the operation keys. The operator caneven discern the operation keys in a dark environment in accordance withthe above structure.

The operator can appropriately change the direction of the imagesdisplayed in the display portion, and can appropriately change thedirection of the images such as characters, symbols, and numeralsdisplayed in the operation keys, in accordance with the portableinformation terminal usage. The ease of use of the portable informationterminal can be improved with the above structure.

Further, the portable information terminal of the present invention mayalso use a structure having a CCD camera. By using the CCD camera, theoperator can send image information, taken in as electronic data to theportable image terminal by the CCD camera, to other persons on the spot.

Structures of the present invention are shown below.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising: a display portion; anaudio input portion; an audio output portion; and operation keys;

characterized in that:

the display portion has active elements;

the operation keys have LEDs; and

the direction of an image displayed by the LEDs is switchable.

An electronic device may be characterized in that the active element hasEL or liquid crystals.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising: a display portion; anaudio input portion; an audio output portion; and operation keys;

characterized in that:

the display portion has EL elements;

the operation keys have liquid crystals; and

the direction of an image displayed by the liquid crystals isswitchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the display portion has EL elements;

the operation keys have LEDs; and

the direction of an image displayed by the LEDs is switchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the display portion has EL elements;

the operation keys have liquid crystals; and

the direction of an image displayed by the liquid crystals isswitchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the display portion has EL elements;

the operation keys have LEDs;

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the direction of an image displayed by the LEDs is switchable inaccordance with the angle between the first panel and the second panel.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the display portion has EL elements;

the operation keys have liquid crystals;

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the direction of an image displayed by the liquid crystals is switchablein accordance with the angle between the first panel and the secondpanel.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the display portion has a plurality of pixels;

the plurality of pixels each have: a photodiode; an EL element; aswitching TFT; an EL driver TFT; a reset TFT; a buffer TFT; and aselection TFT;

the switching TFT and the EL driver TFT control light emission from theEL element;

light emitted from the EL elements is reflected upon a subject andirradiated onto the photodiodes;

the photodiodes, the reset TFTs, the buffer TFTs, and the selection TFTsgenerate an image signal from the light irradiated onto the photodiodes;

the operation keys have LEDs; and

the direction of an image displayed by the LEDs is switchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the display portion has a plurality of pixels;

the plurality of pixels each have: a photodiode; an EL element; aswitching TFT; an EL driver TFT; a reset TFT; a buffer TFT; and aselection TFT;

the switching TFT and the EL driver TFT control light emission from theEL element;

light emitted from the EL elements is reflected upon a subject andirradiated onto the photodiodes;

the photodiodes, the reset TFTs, the buffer TFTs, and the selection TFTsgenerate an image signal from the light irradiated onto the photodiodes;

the operation keys have liquid crystals; and

the direction of an image displayed by the liquid crystals isswitchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising: a display portion; anaudio input portion; an audio output portion; and operation keys;

characterized in that:

the display portion have first EL elements;

the operation keys have second EL element; and

the direction of an image displayed by the second EL elements isswitchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the display portion has first EL elements;

the operation keys have second EL elements; and

the direction of an image displayed by second EL elements is switchable.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the display portion has first EL elements;

the operation keys have second EL elements;

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed; and

the direction of an image displayed by second EL elements is switchablein accordance with the angle between the first panel and the secondpanel.

According to the present invention, there is provided an electronicdevice functioning as a telephone, comprising:

a first panel having: one of an audio input portion and an audio outputportion; and a display portion;

a second panel having: one of an audio input portion and an audio outputportion; and operation keys;

characterized in that:

the first panel and the second panel are connected;

the angle between the first panel and the second panel can bearbitrarily changed;

the display portion has a plurality of pixels;

the plurality of pixels each have: a photodiode; a first EL element; aswitching TFT; an EL driver TFT; a reset TFT; a buffer TFT; and aselection TFT;

the switching TFT and the EL driver TFT control light emission from thefirst EL element;

light emitted from the first EL elements is reflected upon a subject andirradiated onto the photodiodes;

the photodiodes, the reset TFTs, the buffer TFTs, and the selection TFTsgenerate an image signal from the light irradiated onto the photodiodes;

the operation keys have second EL elements; and

the direction of an image displayed by the second EL elements isswitchable.

An electronic device may be characterized in that the first EL elementseach have an anode, a cathode, and an EL layer formed between the anodeand the cathode; and

the external quantum efficiency of the EL layer is equal to or greaterthan 10%.

An electronic device may be characterized in that the maximum value ofthe strength of light emitted by the first EL elements is equal to orgreater than 251 m/W.

An electronic device may be characterized in that the second EL elementseach have an anode, a cathode, and an EL layer formed between the anodeand the cathode; and

the external quantum efficiency of the EL layer is equal to or greaterthan 10%.

An electronic device may be characterized in that the maximum value ofthe strength of light emitted by the second EL elements is equal to orgreater than 251 m/W.

An electronic device may be characterized by having a CCD lightreceiving portion.

An electronic device may be characterized in that an image is taken inas electronic date in the CCD light receiving portion.

An electronic device may be characterized in that:

the display portion has a touch panel; and

an image written into the touch panel is read in as electronic data.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are external views of a portable information terminal ofthe present invention;

FIGS. 2A and 2B are blow up diagrams of an operation panel of a portableinformation terminal of the present invention;

FIGS. 3A and 3B are top surface diagrams of a portable informationterminal of the present invention;

FIGS. 4A and 4B are external views of a portable information terminal ofthe present invention;

FIGS. 5A and 5B are a blow up diagram of operation keys and a drivercircuit, respectively, of a portable information terminal of the presentinvention;

FIG. 6 is a circuit diagram of an EL display device used in a displayportion of a portable information terminal of the present invention;

FIG. 7 is a top surface diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

FIG. 8 is a timing chart showing a method of driving an EL displaydevice used in a display portion of a portable information terminal ofthe present invention;

FIG. 9 is a top surface diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

FIG. 10 is a timing chart of a method of driving an EL display deviceused in a display portion of a portable information terminal of thepresent invention;

FIG. 11 is a top surface diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

FIG. 12 is a circuit diagram of an EL display device used in a displayportion of a portable information terminal of the present invention;

FIG. 13 is a timing chart showing a method of driving an EL displaydevice used in a display portion of a portable information terminal ofthe present invention;

FIGS. 14A to 14D are diagrams showing a method of manufacturing an ELdisplay device used in a display portion of a portable informationterminal of the present invention;

FIGS. 15A to 15C are diagrams showing the method of manufacturing the ELdisplay device used in the display portion of the portable informationterminal of the present invention;

FIG. 16A to 16C are diagrams showing the method of manufacturing the ELdisplay device used in the display portion of the portable informationterminal of the present invention;

FIGS. 17A and 17B are diagrams showing the method of manufacturing theEL display device used in the display portion of the portableinformation terminal of the present invention;

FIGS. 18A and 18B are diagrams showing a mounting position of a touchpanel and a touch panel structure;

FIG. 19 is a circuit diagram of an EL display device used in a displayportion of a portable information terminal of the present invention;

FIG. 20 is a circuit diagram of a pixel of an EL display device used ina display portion of a portable information terminal of the presentinvention;

FIGS. 21A and 21B are external diagrams of an EL display device used ina display portion of a portable information terminal of the presentinvention;

FIG. 22 is a cross sectional diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

FIGS. 23A and 23B are a top surface view and a circuit diagram,respectively, of a pixel of an EL display device used in a displayportion of a portable information terminal of the present invention;

FIG. 24 is a cross sectional diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

FIG. 25 is a diagram of a conventional portable telephone;

FIG. 26 is a cross sectional diagram of a passive type EL displaydevice;

FIG. 27 is a circuit diagram of a liquid crystal display device; and

FIGS. 28A to 28C are cross sectional diagrams of a connection portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

An example of a structure of a portable information terminal of thepresent invention is shown in FIG. 1A. Reference numeral 101 denotes adisplay panel, and reference numeral 102 denotes an operation panel. Thedisplay panel 101 and the operation panel 102 are connected in aconnection portion 103. An angle θ between a plane in which a displayportion 104 of the display panel 101 is formed, and a plane in whichoperation keys 106 of the operation panel 102 are formed, can then bearbitrarily changed.

A structure of the portable information terminal in a state in which thedisplay panel 101 and the operation panel 102 overlap is shown in FIG.1B. In this case, the angle θ becomes 0°.

The display panel 101 has the display portion 104. Further, the displayportion 101 has an audio output portion 105, and audio is output fromthe audio output portion 105. The display portion 104 of the portableinformation terminal of the present invention is structured by: an ELdisplay device using an active element (EL element) having a layercontaining an organic compound (hereafter referred to as organiccompound layer) in which luminescence is generated by application of anelectric field; or a liquid crystal display device using an activeelement having liquid crystals.

The EL display device is also referred to as an organic EL display(OELD) and an organic light emitting diode (OLED). The EL displaydevice, differing from the liquid crystal display device, is a selflight emitting type. EL elements have a structure in which a layercontaining an organic compound which generated luminescence by applyingan electric field (hereafter referred to as organic substance layer) issandwiched between a pair of electrodes (an anode and a cathode), andthe organic compound layer usually has a lamination structure. Alamination structure of a hole transporting layer, a light emittinglayer, and an electron transporting layer developed by Tang, et al., ofEastman Kodak Company can be given as a typical lamination structure.This structure has extremely high light emitting efficiency, and most ofthe EL display devices currently being researched and developed employthis structure.

Electroluminescence generated by the application of an electric field isobtained in the EL element, which has an anode layer, an organiccompound layer, and a cathode layer. There is emission of light in theluminescence of the organic compound when returning to a ground statefrom a singlet excitation state (fluorescence), and when returning to aground state from a triplet excitation state (phosphorescence), and thelight emitting device of the present invention may use both types oflight emission.

Further, a structure in which a hole injecting layer, a holetransporting layer, a light emitting layer, and an electron transportinglayer are laminated in order on an electrode; and a structure in which ahole injecting layer, a hole transporting layer, a light emitting layer,an electron transporting layer, and an electron injecting layer arelaminated in order on an electrode may also be used. Doping of amaterial such as a fluorescent pigment into the light emitting layer mayalso be performed.

All layers formed between one pair of electrodes are referred togenerically as organic compound layers within this specification. Theabove stated hole injecting layer, hole transporting layer, lightemitting layer, electron transporting layer, electron injecting layer,and the like are therefore all contained within the organic compoundlayer.

Elements formed by an anode, an organic compound layer, and a cathodeare referred to as EL elements in this specification.

The operation panel 102 has the operation keys 106, a power sourceswitch 107, an audio input portion 108, and a CCD light receivingportion 109. Note that, although the operation keys 106 and the powersource switch 107 are formed separately in this embodiment mode, astructure in which the power source switch 107 is contained within theoperation keys 106 may also be used.

Audio is input in the audio input portion 107. An image input in the CCDlight receiving portion 109 is taken in as electronic data by theportable information terminal.

Note that, although the display panel 101 has the audio output portion105 in FIGS. 1A and 1B, and the operation panel has the audio inputportion 108, the present invention is not limited to this structure. Thedisplay panel 101 may have the audio input portion 108, and theoperation panel may have the audio output portion 105. Further, both theaudio output portion 105 and the audio input portion 108 may be formedtogether in the display panel 101, and both the audio output portion 105and the audio input portion 108 may be formed together in the operationpanel 102.

Furthermore, the portable information terminal of the present inventionhas the operation keys 106 each having a means of display such as anLED, a liquid crystal display device, or an EL display device.Characters, symbols, numerals, and the like are displayed in therespective operation keys 106 by the LEDs, liquid crystal displaydevices, or EL display devices of each operation key 106.

Note that the portable information terminal does not have an antenna inthis embodiment mode, but an antenna may also be formed when necessary.

FIGS. 2A and 2B show an enlarged diagram of the operation panel 102.Portions which are the same as those shown in FIGS. 1A and 1B use thesame reference symbols.

The operation keys 106 shown in FIG. 2A display a single number, or aplurality of, characters, symbols, numerals, and the like in a blackcolor on a white color background. The operation keys 106 shown in FIG.2B display a single number, or a plurality of, characters, symbols,numerals, and the like in a white color on a black color background.

Note that, although the operation keys performing display by black orwhite colors is explained with FIG. 2A and FIG. 2B, the presentinvention is not limited to this. The operation keys may also performdisplay of a color other than white. For example, yellow color displayon a black color background, green color display on a white colorbackground, and black color display on a blue color background may alsobe performed.

Further, with the portable information terminal of the presentinvention, it is possible for an operator to suitably change thedirection of an image displayed in the display portion 104, and thedirection of images such as characters, numerals, and symbols displayedin the operation keys 106. FIGS. 3A and 3B show top surface views of aportable information terminal.

FIG. 3A shows a case of original directions seen from the operator, forthe direction of the image displayed in the display portion 104 and thedirection of the images such as characters, numerals, and symbolsdisplayed in the operation keys 106, when the display panel 101 and theoperation panel 102 are placed next to each other horizontally.

FIG. 3B shows a case of original directions seen from the operator, forthe direction of the image displayed in the display portion 104 and thedirection of the images such as characters, numerals, and symbolsdisplayed in the operation keys 106, when the display panel 101 and theoperation panel 102 are placed next to each other vertically.

With the portable information terminal of the present invention, it ispossible to switch between the direction shown in FIG. 3A and thedirection shown in FIG. 3B, in accordance with the preference of theoperator regarding ease of use, for the direction of the image displayedin the display portion 104 and the direction of the images such ascharacters, numerals, and symbols displayed in the operation keys 106.

Note that, although a case in which the direction of the image displayedin the display portion 104, and the direction of the images such ascharacters, numerals, and symbols displayed in the operation keys 106,are always the same is explained with FIGS. 2A and 2B, the presentinvention is not limited to this. The directions of the image displayedin the display portion 104 and the direction of the images such ascharacters, numerals, and symbols displayed in the operation keys 106may also differ.

Note that one example of images such as characters, numerals, andsymbols displayed in the operation keys is shown in FIGS. 2A and 2B, andthat the portable information terminal of the present invention is notlimited to those characters, numerals, and symbols.

Further, a structure in which the direction of the images displayed inthe display portion 104 and the direction of the images such ascharacters, numerals, and symbols displayed in the operation keys 106can be automatically changed in accordance with an angle θ between aplane having the display portion 104 of the display panel 101, and aplane having the operation keys 106 of the operation panel 102, in theconnection portion 103.

For example, for a case in which the angle θ is equal to or greater than180°, as shown in FIG. 4A, the direction of the image displayed in thedisplay portion 104 and the direction of the images such as characters,numerals, and symbols displayed in the operation keys 106 switches tothe direction shown in FIG. 3A. Then, for a case in which the angle θ isgreater than or equal to 0° and less than or equal to 180°, thedirection of the image displayed in the display portion 104 and thedirection of the images such as characters, numerals, and symbolsdisplayed in the operation keys 106 switch to the direction shown inFIG. 3B.

The portable information terminal of the present invention can thus bemade into a device which is easy to use for the operator in accordancewith the above structure.

EMBODIMENTS

Embodiments of the present invention are explained below.

Embodiment 1

A structure of operation keys of a portable information terminal of thepresent invention is explained in detail in Embodiment 1.

A blow up diagram of the operation keys of the portable informationterminal of the present embodiment is shown in FIG. 5A. The operationkeys of Embodiment 1 have a total of 8×8 pixels in which eight columnsx1 to x8 and eight rows y1 to y8 are arranged in a matrix shape. Notethat, although a structure having a total of 8×8 pixels is shown inEmbodiment 1, the present invention is not limited to this. The numberof pixels of the operation keys can be suitably determined by a userimplementing the present invention.

FIG. 5B shows a driver circuit group of the operation keys of theportable information terminal shown in FIG. 5A. Reference numeral 151denotes a column driver circuit, and the column driver circuit inputsdisplay data to each of the eight columns of pixels x1 to x8. Referencenumeral 152 denotes a row driver circuit, and the row driver circuitselects the eight rows y1 to y8 in order so that the display data inputto the eight columns x1 to x8 is input to designated pixels.

Each pixel of the operation keys has an LED, an EL display device, or aliquid crystal display device.

The display data is stored in a first memory 153 and a second memory154, respectively. By selecting one of the first memory 153 and thesecond memory 154, the display data stored in the selected memory isinput to the column driver circuit 151.

The images such as characters, numerals, and symbols displayed in theoperation keys in accordance with the display data stored in the firstmemory 153, and the images such as characters, numerals, and symbolsdisplayed in the operation keys in accordance with the display datastored in the second memory 154 have mutually differing directions.

Note that, although an example having two memories for storing thedisplay data is shown in Embodiment 1, the present invention is notlimited to this structure. The portable information terminal of thepresent invention may have two, or more than two, memories for storingthe display data.

Further, the operation key memories or the operation key driver circuitgroup may also be contained within a component such as a microchip or anLSI within the portable information terminal. In addition, a dedicatedLSI may also be formed for the operation key memories or the operationkey driver circuit group.

Further, it is not necessary for the operation keys to always performdisplay, and a structure in which light is emitted and display isperformed only when required may also be used. For example, when theportable information terminal is utilized as a portable telephone,display may be performed in all of the operation keys only within afixed period when any one of the operation keys is pressed. If theportable information terminal is used as a mobile computer, display maybe always performed in the operation keys even when there is no input tothe operation keys because it is necessary for the operator to always beable to differentiate between the operation keys. Electric powerconsumption can be suppressed in accordance with the above structure.

Embodiment 2

A structure of an EL display device used in a display portion of aportable information terminal of the present invention is explained indetail in Embodiment 2.

The portable information terminal of Embodiment 2 uses an EL displaydevice in a display portion, and therefore it is not necessary to use abacklight, differing from a portable information terminal using a liquidcrystal display device. The portable information terminal canconsequently be made smaller, lighter, and thinner. The EL displaydevice is a self light emitting type display device, and therefore has awider angle of view compared with the liquid crystal display device.

FIG. 6 shows a structure of the pixel portion of the EL display deviceof Embodiment 2. Reference numeral 600 denotes a display portion, andthe display portion has source signal lines S1 to Sx, electric powersource supply lines V1 to Vx, and gate signal lines G1 to Gy. A regioncontaining one of the source signal lines S1 to Sx, one of the electricpower source supply lines V1 to Vx, and one of the gate signal lines G1to Gy is a pixel 602.

The pixel 602 has a switching TFT 602, an EL driver TFT 603, an ELelement 604, and a storage capacitor 605. Note that, although astructure having the storage capacitor 605 is shown in Embodiment 2, thepresent invention is not limited to this structure, and a structure inwhich the storage capacitor 605 is not formed may also be used.

A gate electrode of the switching TFT 602 is connected to any one of thegate signal lines G1 to Gy. Further, one of a source region and a drainregion of the switching TFT 602 is connected to one of the source signallines S1 to Sx, while the other is connected to a gate electrode of theEL driver TFT 603 and to the storage capacitor 605, respectively.

A source region of the EL driver TFT 603 is connected to any one of theelectric power source supply lines V1 to Vx. Further, a drain region ofthe EL driver TFT 603 is connected to one of an anode and a cathode ofthe EL element 604.

Note that n-channel TFTs and p-channel TFTs may be used for theswitching TFT 602 and for the EL driver TFT 603. However, in a case thedrain region of the EL driver TFT 603 is connected to the anode of theEL element 604, it is preferable that the EL driver TFT 603 be ap-channel TFT. Conversely, in a case the drain region of the EL driverTFT 603 is connected to the cathode of the EL element 604, it ispreferable that the EL driver TFT 603 be an n-channel TFT.

Embodiment 3

An example of a driver circuit of the EL display device shown byEmbodiment 2 is explained in Embodiment 3.

FIG. 7 shows a block diagram of the EL display device of Embodiment 3.Reference numeral 620 denotes a source signal line driver circuit, andreference numeral 622 denotes a gate signal line driver circuit, andboth of the driver circuits control the driving of the switching TFT 602and the EL driver TFT 603.

The source signal line driver circuit 620 has a shift register 620 a, alatch (A) 620 b, and a latch (B) 620 c. A clock signal CLK and a startpulse SP are input to the shift register 620 a in the source signal linedriver circuit 620. The shift register 620 a generates timing signals inorder based upon the clock signal CLK and the start pulse SP, andsupplies the timing signals one after another to downstream circuits.

Note that the timing signals from the shift register circuit 620 a maybe buffer amplified by a circuit such as a buffer (not shown in thefigure) and then supplied one after another to the downstream circuitsas buffer amplified timing signals. The load capacitance (parasiticcapacitance) of a wiring which supplies the timing signals is largebecause many of the circuits and elements are connected to the wiring.The buffer is formed in order to prevent bluntness in the rise and fallof the timing signal, generated due to the large load capacitance.

The timing signals from the shift register 620 a are supplied to thelatch (A) 620 b. The latch (A) 620 b has a plurality of latch stages forprocessing digital data signals containing image information. The latch(A) 620 b writes in and maintains a digital signal simultaneously withthe input of the timing signal.

Note that the digital data signal may also be input in order to theplurality of latch stages of the latch (A) 620 b when writing in thedigital data signal to the latch (A) 620 b. However, the presentinvention is not limited to this structure. The plurality of latchstages of the latch (A) 620 b may be divided into a number of groups,and the digital data signal may be input to the respective groups at thesame time in parallel, performing partitioned driving. Note that, atthis time the number of groups is referred to as partitioned number. Forexample, this is referred to as partitioned drive with 4 divisions whenthe latches are divided into groups every four stages.

The period until the digital data signal is completely written into allof the latch stages of the latch (A) 620 b is referred to as a lineperiod. Namely, the line period begins at the point when the digitaldata signal is written into the leftmost stage latch within the latch(A) 620 b, and is completed when the digital data signal is written intothe rightmost stage latch. In practice, there are times when the lineperiod includes the addition of a horizontal return period to the aboveline period.

A latch signal is supplied to the latch (B) 620 c when one line periodis complete. The digital data signal written into and stored in thelatch (A) 620 b is sent all at once at this instant to the latch (B) 620c, and is written into all of the stage latches of the latch (B) 620 c,and stored.

Write in of the digital data signal is again performed, in order, to thelatch (A) 620 b after it has completed sending the digital data signalto the latch (B) 620 c, based on the timing signal from the shiftregister 620 a.

The digital data signal written into and stored in the latch (B) 620 bis input to source signal lines S1 to Sx during the second one lineperiod.

On the other hand, the gate signal line driver circuit 622 has a shiftregister and a buffer, respectively (both not shown in the figure).Further, the gate signal line driver circuit 622 may also have a levelshifter in addition to the shift register and the buffer, depending uponthe circumstances.

A gate signal from the shift register (not shown in the figure) suppliedto the buffer (not shown in the figure), and is supplied to thecorresponding gate signal line in the gate signal line driver circuit622. The gate electrodes of the switching TFTs 602 for one line portionof pixels are connected to the gate signal lines G1 to Gy, and theswitching TFTs 602 of all of the one line portion of pixels must beplaced in an ON state simultaneously. A circuit in which a largeelectric current is capable of flowing is therefore used in the buffer.

Note that the number, structure, and operation of the source signal linedriver circuits and the gate signal line driver circuits is not limitedto the structure shown by Embodiment 3. It is also possible to use knownsource signal line driver circuits and known gate signal line drivercircuits for the EL display device of Embodiment 3.

A timing chart for a case of performing 2⁶ gray scale display by the ELdisplay device of Embodiment 3 and in accordance with a display periodseparated driving method, one type of time partitioned driving, is shownin FIG. 8. Note that, although an example of performing 2⁶ gray scaledisplay is shown by Embodiment 3, Embodiment 3 is not limited to 2⁶ grayscales, and it is possible for the implementor to suitably determine thenumber of digital signal bits.

Time is shown in the horizontal axis in the timing chart of FIG. 8,while the position of the gate signal lines is shown in the verticalaxis.

One frame period is divided into six subframe periods SF1 to SF6. Notethat a period during which one image is displayed in all of the pixelsof the display portion is referred to as one frame period F. A normal ELdisplay device operates with an oscillation frequency equal to orgreater than 60 Hz; namely, 60 or more frame periods are formed in onesecond, and 60 or more images are displayed in one second. If the numberof images displayed during one second becomes fewer than 60, imageflicker or the like begins to become visually conspicuous. Note that theplurality of periods into which one frame period is divided are referredto as subframe periods. The number of divisions of one frame periodincreases along with greater numbers of gray scales, and the drivercircuit must be driven at high frequency.

One subframe period is divided into a write in period Ta and a displayperiod Ts. The write in period is a period within one subframe periodduring which a digital signal is input to all of the pixels. The displayperiod (also referred to as turn on period) is a period during which theEL elements are selected to be in a light emitting state or a non-lightemitting state, and display is performed.

The length of the write in periods Ta1 to Ta6 of the n subframe periodsSF1 to SF6, respectively, are all fixed. The display periods Ts of thesubframe periods SF1 to SF6 become display periods Ts1 to Ts6,respectively.

The length of the display periods is set so as to become Ts1::Ts2::Ts3::. . . ::Ts6=2⁰::2¹::2²:: . . . ::2⁵. Note that the subframe periods SF1to SF6 may be appear in any order. By combining the display periods, adesired gray scale display can be performed from among 2⁶ gray scales.

First, in the write in period, the electric potential (electric powersource electric potential) of the electric power source supply lines V1to Vx is maintained at the same height as the electric potential of anopposing electrode (opposing electric potential). The height of theelectric power source electric potential may be set to the same heightas the opposing electric potential within a range in which the ELelements do not emit light. Note that the electric power source electricpotential is always maintained at a fixed level. Further, the electricpotential difference between the opposing electric potential and theelectric power source electric potential is referred to as an EL drivervoltage. It is preferable that the EL driver voltage be 0 V during thewrite in period, but it may have any size such that the EL elements donot emit light.

All of the switching TFTs 602 connected to the gate signal line G1 areplaced into an ON state by the gate signal input to the gate signal lineG1. A digital data signal is input into the source signal lines (S1 toSx) at the same time. The digital data signal contains “0” and “1”information, and one of the digital data signals “0” and “1” has HIelectric voltage, while the other has LO voltage.

The digital signal input into the source signal lines (S1 to Sx) is theninput to the gate electrodes of the EL driver TFTs 603 through theswitching TFTs 602, which are in the ON state.

Next, by the gate signal input to the gate signal line G2, all of theswitching TFTs 602 connected to the gate signal line G2 are placed inthe ON state. The digital signal is then input to the source signallines (S1 to Sx).

The digital data signal input to the source signal lines (S1 to Sx) isinput to the gate electrodes of the EL driver TFTs 603 through theswitching TFTs 602 in the ON state.

By repeating the above operations for the gate signal lines G3 to Gy,the digital data signal is input to the gate electrodes of the EL driverTFTs of all of the pixels. The period up until the digital data signalis input to the gate electrode of the EL driver TFT 603 of all of thepixels is the write in period.

The display period commences at same time as when the write in period iscomplete. All of the switching TFTs 602 are set into the OFF state inthe display period. The electric power source electric potential is thenset so as to have an electric potential difference with the opposingelectric potential on an order such that the EL elements 604 emit light.

When the digital signal input to the gate electrode of the EL driverTFTs 603 has “0” information, the EL driver TFTs 603 are set into theOFF state in Embodiment 3. The pixel electrodes of the EL elements 604are therefore maintained at an electric potential which has the sameheight as the opposing electric potential. As a result, the EL elements604 having pixels to which the digital signal containing “0” informationis applied do not emit light.

Conversely, in this embodiment, the EL driver TFTs 603 are placed intothe ON state in a case the digital signal has “1” information. Theelectric potential of the pixel electrodes of the EL elements 604 aretherefore maintained at the electric power source electric potential.Further, the opposing electric potential has an electric potentialdifference with the electric power source electric potential on an ordersuch that the EL elements 604 emit light. As a result, the EL elements604 having pixels to which the digital signal containing “1” informationis applied emit light.

Note that, although the EL driver TFTs 603 are in the OFF state in acase the digital signal has “0” information, and although the EL driverTFTs 603 are in the ON state when the digital signal has “1” informationin Embodiment 3, the present invention is not limited to this structure.A structure in which the EL driver TFTs 603 are placed in the ON statewhen the digital signal has “0” information, and in which the EL driverTFTs 603 are placed in the OFF state when the digital signal has “1”information may also be used.

Whether the EL elements are placed in a state of emitting light or notemitting light is thus selected in accordance with the information inthe digital signal, and display is performed in all of the pixels atonce. An image is formed by performing display in all of the pixels. Theperiod during which the pixels perform display is referred to as thedisplay period.

The display period is any of the display periods Ts1 to Ts6.Predetermined pixels are turned on in the display period Ts1 here.

Next, the write in period is entered again, and the display periodbegins once the digital signal is input to all of the pixels. At thispoint the display period becomes any of the display periods Ts2 to Ts6.Predetermined pixels are turned on in the display period Ts2 here.

Similar operations are subsequently repeated in the four remainingsubframe periods, and predetermined pixels are turned on in the displayperiods within the respective subframe periods.

One frame period ends when the six subframe periods appear. The grayscale of each pixel is determined by adding the lengths of the displayperiods in which each pixels is turned on.

Note that the EL display device controls the emission of light from theEL elements in Embodiment 3 by always maintaining the opposing electricpotential at a fixed electric potential, changing the write in periodsand the display periods, and changing the size of the EL driver voltage.However, the present invention is not limited to this structure. The ELdisplay device of the present invention may also control the lightemission of the EL elements by always maintaining a fixed electric powersource electric potential and changing the opposing electric potential.

The source signal line driver circuit 620 and the gate signal linedriver circuit 622 may also be mounted on the substrate on which thedisplay portion 600 is formed in Embodiment 3 by using a component suchas an IC chip. In this case, the structure becomes one in which thesource signal line driver circuit 620 and the gate signal line drivercircuit 622 on the IC chip are connected to the display portion 600through a connector such as an FPC or TAB. The EL display devicecontains the source signal line driver circuit 620 and the gate signalline driver circuit 622 on the IC chip in this case.

Note that it is possible to implement Embodiment 3 by freely combiningit with Embodiment 1 or Embodiment 2.

Embodiment 4

An example of a driver circuit of the EL display device shown byEmbodiment 2 is explained in Embodiment 4.

FIG. 9 shows a top surface view of an EL display device of Embodiment 4.Reference numeral 630 denotes a source signal line driver circuit,reference numeral 632 denotes a gate signal line driver circuit, andreference numeral 600 denotes the display portion. One each of thesource signal line driver circuit and the gate signal line drivercircuit are formed in Embodiment 4, but the present invention is notlimited to this structure. Two source signal line driver circuits may beformed, and two gate signal line driver circuits may also be formed. Thesource signal line driver circuit 630 has a shift register 630 a, alevel shift 630 b, and a sampling circuit 630 c. Note that the levelshift 630 b may be used when necessary, and need not always be used.Further, the structure in Embodiment 4 has the level shift 630 b formedbetween the shift register 630 a and the sampling circuit 630 c, butEmbodiment 4 is not limited to this structure. A structure in which thelevel shift 630 b is incorporated within the shift register 630 a mayalso be used.

Electric power source supply lines V1 to Vx are maintained at a fixedelectric potential (electric power supply electric potential) by beingconnected to an electric power source.

Further, the gate signal line driver circuit 632 has a shift registerand a buffer (both not shown in the figure). The gate signal line drivercircuit 632 may also have a level shift.

A clock signal CLK, which is a panel control signal, and a start pulsesignal SP are input to the shift register 630 a. A sampling signal forsampling an analog signal having image information is output from theshift register 630 a. The output sampling signal is input to the levelshift 630 b, the amplitude of its electric potential is made larger, andthen the sampling signal is output.

The sampling signal output from the level shift 630 b is input to thesampling circuit 630 c. The analog signal is simultaneously input to thesampling circuit 630 c through an analog signal line.

The input analog signal is sampled in accordance with the samplingsignal in the sampling circuit 630 c, and is input to each source signallines S1 to Sx.

A timing chart for a case of driving the EL display device of Embodiment4 by an analog method is shown in FIG. 10. A period from the selectionof one gate signal line until the selection of the next, different gatesignal line is referred to as one line period L. Note that in thisspecification the selection of the gate signal line denotes a gatesignal, having an electric potential such that a switching TFT becomesplaced in the ON state, being input to a gate signal line.

Further, a period from when one image is displayed until the next imageis displayed corresponds to one frame period F. There are y gate signallines in the case of the EL display device of Embodiment 4, andtherefore y line periods L1 to Ly are formed within one frame period.

First, the electric power source electric potential of the electricpower source supply lines V1 to Vx is always maintained at a fixed valuein Embodiment 4. The electric potential of opposing electrodes is alsomaintained at a fixed value. The electric potential of the opposingelectrodes has an electric potential difference with the electric powersource electric potential of an order at which the EL elements emitlight when the electric power source electric potential is imparted topixel electrodes of the EL elements 604.

The gate signal line G1 is selected in the first line period L1 inaccordance with the gate signal input from the gate signal line drivercircuit 632 through the gate signal line G1, and all of the switchingTFTs connected to the gate signal line G1 are placed in the ON state.The analog signal is then input from the source signal line drivercircuit 630 to the source signal lines S1 to Sx in order. The analogsignal input to the source signal lines S1 to Sx is input to the gateelectrodes of the EL driver TFTs 603 through the switching TFTs 602.

The amount of electric current flowing in channel forming regions of theEL driver TFTs 603 is controlled in accordance with a gate voltage Vgs,which is the electric potential difference between gate electrodes andsource regions of the EL driver TFTs 603. The electric potentialimparted to the pixel electrodes of the EL elements 604 is thereforedetermined by the electric potential of the analog signal input to thegate electrodes of the EL driver TFTs 603. The EL elements 604 aretherefore controlled by the electric potential of the analog signal andperforms light emission.

When the above operations are repeated and input of the analog signal tothe source signal lines S1 to Sx is completed, the first line period L1is complete. Note that a period until the completion of the analogsignal input to the source signal lines S1 to Sx may also be combinedwith a horizontal return period and taken as one line period. The secondline period L2 begins next, the gate signal line G2 is selected by thegate signal, and the analog signal is input in order to the sourcesignal lines S1 to Sx, similar to the first line period L1.

All of the line periods L1 to Ly are complete when all of the gatesignal lines G1 to Gy are selected. One frame period is then completewhen all of the line periods L1 to Ly are completed. One image is formedwithin one frame period by performing display in all of the pixels. Notethat all of the line periods L1 to Ly and a horizontal return period mayalso be combined and taken as one frame period.

The amount of light emitted by the EL elements is thus controlled inaccordance with the electric potential of the analog signal, and grayscale display is performed in accordance with the control of the amountof light emitted.

The source signal line driver circuit 630 and the gate signal linedriver circuit 632 may also be mounted on the substrate on which thedisplay portion 600 is formed in Embodiment 4 by using a component suchas an IC chip. In this case, the structure becomes one in which thesource signal line driver circuit 630 and the gate signal line drivercircuit 632 on the IC chip are connected to the display portion 600through a connector such as an FPC or TAB. The EL display devicecontains the source signal line driver circuit 630 and the gate signalline driver circuit 632 on the IC chip in this case.

Note that it is possible to implement Embodiment 4 by freely combiningit with Embodiment 1 or Embodiment 2.

Embodiment 5

An EL display device having a structure which differs from that ofEmbodiments 2 to 4 is explained in Embodiment 5.

An example of a block diagram of an EL display device of the presentinvention is shown in FIG. 11. The EL display device of FIG. 11 has adisplay portion 700 formed on a substrate by TFTs, a source signal linedriver circuit 702 arranged in the periphery of the display portion 700,a write in gate signal line driver circuit (a first gate signal linedriver circuit) 703, and an erasure gate signal line driver circuit (asecond gate signal line driver circuit) 704. Note that, although the ELdisplay device has one source signal line side driver circuit inEmbodiment 5, two source signal line side driver circuits may also beused.

The source signal line driver circuit 702 has at least a shift register702 a, a latch (A) 702 b, and a latch (B) 702 c.

A clock signal CLK and a start pulse SP are input to the shift register702 a in the source signal line driver circuit 702. The shift register702 a generates timing signals in order based upon the clock signal CLKand the start pulse SP, and supplies the timing signals one afteranother to downstream circuits through a circuit such as a buffer (notshown in the figure).

The timing signals from the shift register circuit 702 a may also bebuffer amplified by such as the buffer (not shown in the figure). Theload capacitance (parasitic capacitance) of a wiring which supplies thetiming signals is large because many of the circuits and elements areconnected to the wiring. The buffer is formed in order to preventbluntness in the rise and fall of the timing signal, generated due tothe large load capacitance.

The timing signals from the shift register 702 a are supplied to thelatch (A) 702 b. The latch (A) 702 b has a plurality of latch stages forprocessing n-bit digital data signals containing image information. Thelatch (A) 702 b writes in and maintains an n-bit digital signal suppliedfrom external of the EL display device and simultaneously with the inputof the timing signal.

Note that the digital signal may also be input in order to the pluralityof latch stages of the latch (A) 702 b when writing in the n-bit digitalsignal to the latch (A) 702 b. However, the present invention is notlimited to this structure. The plurality of latch stages of the latch(A) 702 b may be divided into a number of groups, and the digital signalmay be input to the respective groups at the same time in parallel,performing namely partitioned driving. Note that, the number of groupsis called the partitioned number. For example, this is referred to asgray scale drive with 4 divisions when the latches are divided intogroups every four stages.

The period until the digital signal is completely written into all ofthe latch stages of the latch (A) 702 b is referred to as a line period.Namely, the line period begins at the point when the digital signal iswritten into the leftmost stage latch within the latch (A) 702 b, and iscompleted when the digital signal is written into the rightmost stagelatch. In practice, there are times when the line period includes theaddition of a horizontal return period to the above line period.

A latch signal is supplied to the latch (B) 702 c when one line periodis finished. The digital signal written into and stored in the latch (A)702 b is sent all at once at this instant to the latch (B) 702 c, and iswritten into all of the stage latches of the latch (B) 702 c, andstored.

Write in of the digital signal supplied external from the EL displaydevice is again performed, in order, to the latch (A) 702 b after it hascompleted sending the digital signal to the latch (B) 702 c, based onthe timing signal from the shift register 702 a.

The digital signal written into and stored in the latch (B) 702 b isinput to source signal lines S1 to Sx during the second one line period.

On the other hand, the write in gate signal line driver circuit 703 andthe erasure gate signal line driver circuit 704 each have a shiftregister and a buffer (both not shown in the figure). Further, the writein gate signal line driver circuit 703 and the erasure gate signal linedriver circuit 704 may also have a level shifter in addition to theshift register and the buffer, depending upon the circumstances.

A timing signal is supplied from the shift registers (not shown in thefigure) to the buffers (not shown in the figure) in the write-in gatesignal line driver circuit 703 and the erasure gate signal line drivercircuit 704, and then is supplied to the corresponding gate signal lines(also referred to as scanning lines). The gate electrodes of one lineportion of pixel TFTs are connected to the gate signal line, and the oneline portion of pixel TFTs must all be placed in an ON statesimultaneously. A circuit in which a large electric current is capableof flowing is therefore used in the buffer.

The source signal line driver circuit 702, the write in gate signal linedriver circuit 703, and the erasure gate signal line driver circuit 704may also be formed in the substrate on which the display portion 700 isformed in Embodiment 5 or by using a component such as an IC chip tomount on a substrate with a display portion 700. In this case, thestructure becomes one in which the source signal line driver circuit702, the write in gate signal line driver circuit 703, and the erasuregate signal line driver circuit 704 on the IC chip are connected to thedisplay portion 700 through a connector such as an FPC or TAB. The ELdisplay device contains the source signal line driver circuit 702, thewrite in gate signal line driver circuit 703, and the erasure gatesignal line driver circuit 704 on the IC chip in this case.

FIG. 12 shows a blow up of the display portion 700. The source signallines S1 to Sx connected to the latch (B) 702 c of the source signalline driver circuit 702; electric power source supply lines V1 to Vxconnected to an electric power source external to the EL display device;write in gate signal lines (first gate signal lines) Ga1 to Gayconnected to the write in gate signal line driver circuit 703; anderasure gate signal lines (second gate signal lines) Ge1 to Geyconnected to the erasure gate signal line driver circuit 704 are formedin the display portion 700.

A region containing one each of: the source signal lines S1 to Sx; theelectric power source supply lines V1 to Vx; the write in gate signallines Ga1 to Gay; and the erasure gate signal lines Ge1 to Gey is apixel 705. A plurality of the pixels 705 are arranged in a matrix shapein the display portion 700.

Reference numeral 707 within the pixel 705 denotes a switching TFT. Agate electrode of the switching TFT 707 is connected to one of the writein gate signal lines Ga1 to Gay. One of a source region and a drainregion of the switching TFT 707 is connected to one of the source signallines S1 to Sx, and the other is connected to a gate electrode of an ELdriver TFT 708 and to a storage capacitor 712. Further, the storagecapacitor 712 is connected to one of the electric power source supplylines V1 to Vx.

The storage capacitor 712 is formed in order to maintain the gatevoltage of the EL driver TFT 708 when the switching TFT 707 is in anon-selected state (OFF state). Note that, although a structure in whichthe storage capacitor 712 is formed is shown in Embodiment 5, thepresent invention is not limited to this structure, and a structure inwhich the storage capacitor 712 is not formed may also be used.

Further, a source region of the EL driver TFT 708 is connected to one ofthe electric power source supply lines V1 to Vx, and a drain region isconnected to an anode or a cathode of an EL element 710.

One of a source region and a drain region of the erasure TFT 709 isconnected to a gate electrode of the EL driver TFT 708, and the other isconnected to one of the electric power source supply lines V1 to Vx. Agate electrode of the erasure TFT 709 is connected to one of the erasuregate signal lines Ge1 to Gey.

The EL element 710 is composed of an anode, a cathode, and an EL layerformed between the anode and the cathode. When the anode is connected tothe drain region of the EL driver TFT 708, the anode becomes a pixelelectrode and the cathode becomes an opposing electrode. Conversely, ifthe cathode is connected to the drain region of the EL driver TFT 708,then the cathode becomes the pixel electrode and the anode becomes theopposing electrode.

An opposing electric potential is imparted to the opposing electrode ofthe EL element 710. The electric potential difference between theopposing electric potential and the electric power source electricpotential is always maintained in Embodiment 5 at an electric potentialdifference on an order at which the EL element emits light when theelectric power source electric potential is imparted to the pixelelectrode. The electric power source electric potential and the opposingelectric potential are imparted to the EL display device of the presentinvention in accordance with an electric power source formed in acomponent such as an external IC.

In typical EL display devices at present, the necessary amount ofelectric current per surface area of the display portion is on the orderof several mA/cm² when the amount of light emitted per surface area ofthe pixel has a luminescence of 200 cd/m². In particular, therefore, ifthe size of the screen area becomes large, the height of the electricpotential imparted from the electric power source formed in the ICbecomes difficult to control by a switch. The electric power sourceelectric potential and the opposing electric potential are alwaysmaintained as fixed in Embodiment 5, and the height of the electricpotential imparted from the electric power source formed in the IC neednot be controlled by a switch. Embodiment 5 is therefore useful inachieving a panel having a larger screen size.

The switching TFT 707, the EL driver TFT 708, and the erasure TFT 709can either use n-channel TFTs or p-channel TFTs. Further, the switchingTFT 707, the EL driver TFT 708, and the erasure TFT 709 may have, inaddition to a single gate structure, a multi-gate structure such as adouble gate structure of a triple gate structure.

Note that it is preferable that the EL driver TFT 708 be a p-channel TFTfor cases in which the drain region of the EL driver TFT 708 isconnected to the anode of the EL element 710. On the other hand, it ispreferable that the EL driver TFT 708 be an n-channel TFT for cases inwhich the drain region of the EL driver TFT 708 is connected to thecathode of the EL element 710.

Next, a timing chart for a case of performing 2⁶ gray scale display withthe EL display device of Embodiment 5 in accordance with simultaneouserasing scan driving, one method of time partitioned drive, is shown inFIG. 13. Note that, although an example of performing 2⁶ gray scaledisplay is explained by Embodiment 5, the present embodiment is notlimited to 2⁶ gray scales, and it is possible for an operator tosuitably determine the number of digital signal bits.

The horizontal axis shows time and the vertical axis shows gate signallines in the timing chart of FIG. 13.

First, the switching TFTs 707 of all pixels connected to the write ingate signal line Ga1 (a first line of pixels) are placed in the ON statein accordance with a write in gate signal input to the write in gatesignal line Ga1 from the write in gate signal line driver circuit 703.

The first bit of the digital signal is then input simultaneously to thesource signal lines S1 to Sx from the latch (B) 702 c of the sourcesignal line driver circuit 702. The digital signal is input to the gateelectrodes of the EL driver TFTs 708 through the switching TFTs 707. Thedigital signal has “0” or “1” information, and one of the “0” and “1”digital signals is a signal having HI voltage, while the other is asignal having LO voltage.

In a case the digital signal has “0” information, the EL driver TFTs 708are placed in the OFF state in Embodiment 5. The electric power sourceelectric potential is therefore not imparted to the pixel electrode ofthe EL elements 710. As a result, the EL elements 710 of pixels intowhich the digital signals having “0” information are input do not emitlight.

Conversely, the EL driver TFTs 708 are placed in the ON state when adigital signal having “1” information is input. The electric powersource electric potential is therefore imparted to the pixel electrodesof the EL elements 710. As a result, the EL elements 710 of pixels intowhich the digital signals having “1” information are input emit light.

Note that, although the EL driver TFTs 708 are in the OFF state when thedigital signal has “0” information, and although the EL driver TFTs 708are in the ON state when the digital signal has “1” information inEmbodiment 5, the present invention is not limited to this structure. Astructure in which the EL driver TFTs 708 are placed in the ON statewhen the digital signal has “0” information, and in which the EL driverTFTs 708 are placed in the OFF state when the digital signal has □1□information may also be used.

The EL elements 710 are placed in a state of emitting light or notemitting light at the same time that the digital signal is input to thefirst line of pixels, and the first line of pixels perform display. Aperiod during which the pixels perform display is referred to as adisplay period Tr. In particular, the display period which begins byinput of the first bit of the digital signal to the pixels is referredto as a display period Tr1. The timing at which the display periods ofeach line begin have time differences.

Next, the switching TFTs 707 of all pixels connected to the write ingate signal line Ga2 are placed in the ON state in accordance with thewrite in gate signal input to the write in gates signal line Ga2 at thesame time as the selection of the next gate signal line Ga1 iscompleted. The first bit of the digital signal is then input to thesecond line pixels from the source signal lines S1 to Sx.

Note that the input of the signal to the pixels denotes the input of thesignal to the gate electrode of the EL driver TFT through the switchingTFT of the pixel in Embodiment 5.

All of the write in gate signal lines Ga1 to Gax are then selected inorder in accordance with the write in gate signal input to all of thewrite in gate signal lines Ga1 to Gax. The first bit of the digitalsignal is then input to all of the lines of pixels. A period until thefirst bit of the digital signal is input to the pixels of all linesdenotes a write in period Ta1.

On the other hand, before the first bit of the digital signal is inputto all of the lines of pixels, namely before the write in period Ta1 iscomplete, the erasure gate signal line Ge1 is selected in accordancewith an erasure gate signal input from the erasure gate signal linedriver circuit 704 in parallel with the input of the first bit of thedigital signal to the pixels.

The erasure TFTs 709 of all the pixels (the first line of pixels)connected to the erasure gate line Ge1 are then placed in an ON state inaccordance with the erasure gate signal input to the erasure gate signalline Ge1. The electric power source electric potentials of the electricpower source supply lines V1 to Vx are then imparted to the gateelectrodes of the EL driver TFTs 708 through the erasure TFT 709.

The gate electrode and the source region of the EL driver TFT 708 aremaintained at the same electric potential height when the electric powersource electric potential is imparted to the gate electrode of the ELdriver TFT 708, and therefore the EL driver TFTs 708 are place in theOFF state. The electric power source electric potential consequently isnot imparted to the pixel electrodes of the EL elements 710, and all ofthe EL elements of the first line of pixels then become placed in thenon-light emitting state so that the first line of pixels do not performdisplay. In other words, the digital signals stored by the gateelectrodes of the EL driver TFTs 708 from the point at which the writein gate signal line Ga1 is selected in accordance with the write in gatesignal are thus erased by imparting the electric power source electricpotential to the gate electrodes of the EL driver TFTs 708. The firstline of pixels therefore do not perform display.

A period during which the pixels do not perform display is referred toas a non-display period Td. For the first line of pixels, the displayperiod Tr1 is completed at the same time as the erasure gate signal isinput to the erasure gate signal line Ge1, and the non-display periodTd1 thus begins. Then, similar to the display period Tr, the timing atwhich the non-display period Td begins in each line has a timedifferences for each line.

The erasure TFTs 709 of all the pixels (the second line of pixels)connected to the erasure gate signal line Ge2 are then placed in an ONstate in accordance with the erasure gate signal input to the erasuregate signal line Ge2 at the same time as when the selection of Ge1 iscomplete. The electric power source electric potentials of the electricpower source supply lines V1 to Vx are then imparted to the gateelectrodes of the EL driver TFTs 708 through the erasure TFT 709. The ELdriver TFTs 708 are placed in the OFF state when the electric powersource electric potential is imparted to the gate electrodes of the ELdriver TFTs 708. The electric power source electric potential istherefore not imparted to the pixel electrodes of the EL elements 710.As a result, the EL elements of the second line of pixels are all placedin a non-light emitting state, and display is no longer performed in thesecond line of pixels, becoming a non-display state.

The erasure gate signal is the input to all of the erasure gate signallines in order. A period until all of the erasure gate signal lines (Ga1to Gax) are selected and the first bit of the digital signal stored inall the lines of pixels is erased is referred to as an erasure periodTe1.

On the other hand, before the first bit of the digital signal stored inall the lines of pixels is erased, namely before the erasure period Te1is complete, the write in gate signal line Ga1 is selected in accordancewith the write in gate signal input from the write in gate signal linedriver circuit 704. This occurs in parallel with the erasure of thefirst bit of the digital signal in the pixels. Display again isperformed in the first line of pixels as a result, the non-displayperiod Td1 finished, and a display period Tr2 begins.

All of the write in gate signal lines are similarly selected in order,and the second bit of the digital signal is input to all of the pixels.A period until the input of the second bit of the digital signal isfinished to all the lines of pixels is referred to as the write inperiod Ta2.

On the other hand, before the second bit of the digital signal input toall the lines of pixels is erased, namely before the write in period Ta2is complete, the erasure gate signal line Ge2 is selected in accordancewith the erasure gate signal input from the erasure gate signal linedriver circuit 704. This occurs in parallel with the write in of thesecond bit of the digital signal in the pixels. The EL elements of thefirst line of pixels are thus all placed in a non-light emitting state,and the first line of pixels no longer performs display. The displayperiod Tr2 therefore finishes in the first line of pixels, and anon-display period Td2 begins.

The erasure gate signal is then input in order to all of the erasuregate signal lines. A period until all of the erasure gate signal linesGa1 to Gax are selected and the second bit of the digital signal storedin all the lines of pixels is erased is an erasure period Te2.

The above operations are repeatedly performed until the fourth bit ofthe digital signal is input to the pixels, and the display periods Trand the non-display periods Td repeatedly appear. The display period Tr1is the period from when the write in period Ta1 begins until the erasureperiod Te1 begins. Further, the non-display period Td1 is the periodfrom when the erasure period Te1 begins until the display period Tr2begins. Display periods Tr2 and Tr3, and non-display periods Td2 and Td3each then have their periods determined by the write in periods Ta1,Ta2, Ta3, and Ta4, and the erasure periods Te1, Te2, and Te3,respectively, similar to the display period Tr1 and the non-displayperiod Td1.

After an m-th-bit of the digital signal is input to the first line ofpixels, the erasure gate signal lines Ge1 to Gey become unselected inaccordance with the erasure gate signal. For simplicity of explanation,an example of a case in which the erasure gate signal lines Ge1 to Geyare unselected when the fourth bit of the digital signal is input isexplained in Embodiment 5, but the present invention is not limited tothis. Whether the erasure gate signal lines Ge1 to Gey are selected orunselected when a certain bit of the digital signal is input can bearbitrarily selected with the present invention.

A display period Tr4 begins and the first line of pixels perform displaywhen the fourth bit of the digital signal is input to the first line ofpixels. The fourth bit of the digital signal is then stored in thepixels until the next bit of the digital signal is input.

The fourth bit of the digital signal stored in the pixels is replaced bythe fifth bit of the digital signal when the fifth bit of the digitalsignal is then input to the first line of pixels. A display period Tr5thus begins in the first line of pixels, and display is performed. Thefifth bit of the digital signal is stored by the pixels until the nextbit of the digital signal is input.

The fifth bit of the digital signal stored in the pixels is replaced bythe sixth bit of the digital signal when the sixth bit of the digitalsignal is then input to the first line of pixels. A display period Tr6thus begins in the first line of pixels, and display is performed. Thesixth bit of the digital signal is stored by the pixels until the firstbit of the digital signal of the next frame period is input.

The display period Tr4 is the period from when the write in period Ta4begins until the write in period Ta5 begins. The display periods Tr5 andTr6 also have their periods determined similar to that of the displayperiod Tr4, in accordance with the write in periods Ta5, Ta6, and thefirst write in period Ta1 in the next frame period.

Note that it is necessary for the sum of the lengths of all of the writein periods to be shorter than one frame period in Embodiment 5, and inaddition, that the length of the display periods be set so thatTr1::Tr2::Tr3:: . . . :: Tr6=2⁰::2¹::2² . . . ::2⁵. Further, it is veryimportant that the write in periods do not overlap with each other.

One image can be displayed when the display periods Tr1 to Tr6 arecomplete in all of the pixels. The period during which one image isdisplayed is referred to as one frame period F in the driving method ofthe present invention.

After one frame period is complete, a write in gate signal is once againinput to the write in gate signal line Ga1 from the write in gate signalline driver circuit 703. The first bit of the digital signal is input tothe pixels as a result, and the display period Tr1 once again begins inthe first line of pixels. The above stated operations are then repeatedagain.

It is preferable to form 60 or more frame periods every second with anormal EL display device. If the number of images displayed in onesecond becomes fewer than 60, image flicker starts to become visuallyconspicuous.

The gray scale displayed by a pixel during one frame period can be setby finding the total sum of the lengths of the display periods duringwhich the EL element of the pixel emits light during the one frameperiod.

It is vital that the write in period Ta4, in which the fourth bit of thedigital signal is written in to the pixels, be shorter than the lengthof the display period Tr4.

Further, the display periods Tr1 to Tr6 may appear in any order. Forexample, it is possible for the display periods to appear such that Tr3,Tr5, Tr2, . . . , follow after Tr1 within one frame period. However, itis preferable that the erasure periods Te1 to Te6 have an order suchthat they do not overlap with each other.

Non-light emitting periods during which display is not performed can beformed with Embodiment 5. If a completely white image is displayed in anEL display device when using a conventional analog driving method, thenthe EL elements always emit light and this becomes a cause of quickeningEL layer degradation. Non-light emitting periods can be formed with thepresent invention, and therefore degradation of the EL layers can besuppressed to a certain extent.

Note that portions of the display periods Tr and the write in periods Taoverlap in Embodiment 5. In other words, it is possible to have pixeldisplay even during the write in periods Ta. The ratio of the total sumof the lengths of the display periods Tr in one frame period (dutyratio) is therefore determined only by the lengths of the write inperiods Ta.

Note that it is possible to implement Embodiment 5 by freely combiningit with Embodiment 1.

Embodiment 6

In Embodiment 6, a method of manufacturing a display portion having anEL display device, and TFTs (n-channel TFTs and p-channel TFTs) of adriver circuit formed in the periphery of the display portion, on thesame substrate simultaneously is explained in detail.

First, as shown in FIG. 14A, a base film 401 made from an insulatingfilm such as a silicon oxide film, a silicon nitride film, or a siliconnitride oxide film is formed on a substrate 400 made from glass such asbarium borosilicate glass or aluminum borosilicate glass, typicallyCorning Corp. #7059 glass or #1737 glass, or made from a quartzsubstrate. For example, a silicon nitride oxide film made from SiH₄,NH₃, and N₂O by plasma CVD is formed with a thickness of 10 to 200 nm(preferably from 50 to 100 nm), and a hydrogenized silicon nitride oxidefilm with a thickness of 50 to 200 nm (preferably between 100 and 150nm), made from SiH₄ and N₂O, is similarly formed and laminated. Notethat the base film is shown as one layer in FIG. 14A. The base film 401is shown as a two layer structure in Embodiment 6, but it may also beformed as a single layer of the above insulating films, and it may alsobe formed having a lamination structure in which two layers or more arelaminated.

Semiconductor layers 402 to 405 are formed by a crystallinesemiconductor film manufactured using a laser crystallization method ofa semiconductor film having an amorphous structure, or using a knownthermal crystallization method. The thickness of the semiconductorlayers 402 to 405 is formed to a thickness of 25 to 80 nm (preferablybetween 30 and 60 nm). There are no limitations in the crystallinesemiconductor film material, but it is preferable to form the film froma semiconductor material such as silicon or a silicon germanium (SiGe)alloy.

As for known crystallization methods, there is a thermal crystallizationmethod using an electric furnace, a laser annealing crystallizationmethod using laser light, a lamp annealing crystallization method usinginfrared light, and a crystallization method using a catalyst metal.

A laser such as a pulse emission type or continuous emission typeexcimer laser, a YAG laser, and a YVO₄ laser can be used in the lasercrystallization method to manufacture a crystalline semiconductor film.A method of condensing laser light emitted from a laser emission deviceinto a linear shape by an optical system and then irradiating the lightto the semiconductor film may be used when these types of lasers areused. The crystallization conditions may be suitably selected by theoperator, but when using the excimer laser, the pulse emission frequencyis set to 300 Hz, and the laser energy density is set from 100 to 400mJ/cm² (typically between 200 and 300 mJ/cm²). Further, the secondharmonic is utilized when using the YAG laser, the pulse emissionfrequency is set from 30 to 300 KHz, and the laser energy density may beset from 300 to 600 mJ/cm² (typically between 350 and 500 mJ/cm²). Thelaser light collected into a linear shape with a width of 100 to 1000μm, for example 400 μm, is then irradiated over the entire surface ofthe substrate. This is performed with an overlap ratio of 50 to 98% forthe linear shape laser light.

A gate insulating film 406 is formed covering the semiconductor layers402 to 405. A gate insulating film 406 is formed by an insulating filmcontaining silicon with a thickness of 40 to 150 nm by plasma CVD orsputtering. A 120 nm thick silicon nitride oxide film is formed inEmbodiment 6. The gate insulating film 406 is not limited to this typeof silicon nitride oxide film, of course, and other insulating filmscontaining silicon may also be used, in a single layer or in alamination structure. For example, when using a silicon oxide film, itcan be formed by plasma CVD with a mixture of TEOS (tetraethylorthosilicate) and O₂, at a reaction pressure of 40 Pa, with thesubstrate temperature set from 300 to 400° C., and by discharging at ahigh frequency (13.56 MHz) electric power density of 0.5 to 0.8 W/cm².Good characteristics as a gate insulating film can be obtained bysubsequently performing thermal annealing, at between 400 and 500° C.,of the silicon oxide film thus manufactured.

A first conducting film 407 and a second conducting film 408 are thenformed on the gate insulating film 406 in order to form gate electrodes.The first conducting film 407 is formed from Ta (tantalum) with athickness of 50 to 100 nm, and the second conducting film 408 is formedfrom W (tungsten) having a thickness of 100 to 300 nm, in Embodiment 6.

The Ta film is formed by sputtering, and sputtering of a Ta target isperformed by Ar. If appropriate amounts of Xe and Kr are added to Ar atthe time of sputtering, the internal stress of the Ta film is relaxed,and film peeling can be prevented. The resistivity of an α phase Ta filmis on the order of 20 μΩcm, and it can be used in the gate electrode,but the resistivity of a β phase Ta film is on the order of 180 μΩcm andit is unsuitable for the gate electrode. An α phase Ta film can easilybe obtained if a tantalum nitride film, which possesses a crystalstructure near that of α phase Ta, is formed with a thickness of 10 to50 nm as a base for Ta in order to form α phase Ta.

The W film is formed by sputtering with a W target, which can also beformed by thermal CVD using tungsten hexafluoride (WF₆). Whichever isused, it is necessary to be able to make the film become low resistancein order to use it as the gate electrode, and it is preferable that theresistivity of the W film be made equal to or less than 20 μΩcm. Theresistivity can be lowered by enlarging the crystal grains of the Wfilm, but for cases in which there are many impurity elements such asoxygen in the W film, crystallization is inhibited, and the film becomeshigh resistance. A W target having a purity of 99.9999% or 99.99% isthus used in sputtering. In addition, by forming the W film while takingsufficient care that no impurities from within the gas phase areintroduced at the time of film formation, a resistivity of 9 to 20 μΩcmcan be achieved.

Note that, although the first conducting film 407 is Ta and the secondconducting film 408 is W in Embodiment 6, the conducting films are notlimited to these, and both may also be formed from an element selectedfrom the group consisting of Ta, W, Ti, Mo, Al, and Cu, or from an alloymaterial having one of these elements as its main constituent, or from achemical compound of these elements. Further, a semiconductor film,typically a polysilicon film into which an impurity element such asphosphorous is doped, may also be used. Examples of preferablecombinations other than that used in Embodiment 6 include: forming thefirst conducting film by tantalum nitride (TaN) and combining it withthe second conducting film formed from W; forming the first conductingfilm by tantalum nitride (TaN) and combining it with the secondconducting film formed from Al; and forming the first conducting film bytantalum nitride (TaN) and combining it with the second conducting filmformed from Cu. (See FIG. 14B).

Masks 409 to 412 are formed next from resist, and a first etchingprocess is performed in order to form electrodes and wirings. An ICP(inductively coupled plasma) etching method is used in Embodiment 6. Agas mixture of CF₄ and Cl₂ is used as an etching gas, and a plasma isgenerated by applying a 500 W RF electric power (13.56 MHz) to a coilshape electrode at a pressure of 1 Pa. A 100 W RF electric power (13.56MHz) is also applied to the substrate side (test piece stage),effectively applying a negative self-bias voltage. The W film and the Tafilm are both etched on the same order when CF₄ and Cl₂ are combined.

Not shown in FIG. 14C, edge portions of the first conducting layer andthe second conducting layer are made into a tapered shape in accordancewith the effect of the bias voltage applied to the substrate side underthe above etching conditions by using a suitable resist mask shape. Theangle of the tapered portions is from 15 to 45′. The etching time may beincreased by approximately 10 to 20% in order to perform etching withoutany residue remaining on the gate insulating film. The selectivity of asilicon nitride oxide film with respect to a W film is from 2 to 4(typically 3), and therefore approximately 20 to 50 nm of the exposedsurface of the silicon nitride film is etched by this over-etchingprocess. Further, not shown in FIG. 14C, regions of the gate insulatingfilm 406 not covered by first shape conducting layers 414 to 417 aremade thinner by 20 to 50 nm.

The first shape conducting layers 414 to 417 (first conducting layers414 a to 417 a and second conducting layers 414 b to 417 b) are thusformed from the first conducting layer and the second conducting layerin accordance with the first etching process.

A second etching process is performed next, as shown in FIG. 14D. TheICP etching method is similarly used, a mixture of CF₄, Cl₂, and O₂ isused as the etching gas, and a plasma is generated by supplying a 500 WRF electric power (13.56 MHz) to a coil shape electrode at a pressure of1 Pa. A 50 W RF (13.56 MHz) electric power is applied to the substrateside (test stage), and a self-bias voltage which is lower in comparisonto that of the first etching process is applied. The W film is etchedanisotropically under these etching conditions, and Ta (the firstconducting layers) is anisotropically etched at a slower etching speed,forming second shape conducting layers 419 to 422 (first conductinglayers 419 a to 422 a and second conducting layers 419 b to 422 b).Further, although not shown in FIG. 14D, the gate insulating film 406 isadditionally etched on the order of 20 to 50 nm, becoming thinner, inregions not covered by the second shape conducting layers 419 to 422.The masks 409 to 412 are etched by the second etching process, becomingmasks 409 a to 412 a.

The etching reaction of the W film and the Ta film in accordance withthe mixed gas of CF₄ and Cl₂ can be estimated from the radicalsgenerated, and from the ion types and vapor pressures of the reactionproducts. Comparing the vapor pressures of W and Ta fluorides andchlorides, the W fluoride compound WF₆ is extremely high, and the vaporpressures of WCl₅, TaF₅, and TaCl₅ are of similar order. Therefore the Wfilm and the Ta film are both etched by the CF₄ and Cl₂ gas mixture.However, if a suitable quantity of O₂ is added to this gas mixture, CF₄and O₂ react, forming CO and F, and a large amount of F radicals or Fions are generated. As a result, the etching speed of the W film havinga high fluoride vapor pressure becomes fast. On the other hand, even ifF increases, the etching speed of Ta does not relatively increase.Further, Ta easily oxidizes compared to W, and therefore the surface ofTa is oxidized by the addition of O₂. The etching speed of the Ta filmis further reduced because Ta oxides do not react with fluorine andchlorine. It therefore becomes possible to have a difference in etchingspeeds between the W film and the Ta film, and it becomes possible tomake the etching speed of the W film larger than that of the Ta film.

The masks 409 a to 412 a are removed, and a first doping process isperformed as shown in FIG. 15A, adding an impurity element which impartsn-type conductivity. For example, doping may be performed at anacceleration voltage of 70 to 120 keV and with a dosage of 1×10¹³atoms/cm². The doping process is performed using the second shapeconducting layers 419 to 422 as masks against the impurity element, andso as to also add the impurity element in regions below the secondconducting layers 419 a to 422 a. First impurity regions 425 to 428,which overlap with the second conducting layers 419 a to 422 a, andsecond impurity regions 429 to 432, which have a higher impurityconcentration than the first impurity regions, are thus formed. Notethat the n-type conductivity imparting element is added after removingthe masks 409 a to 412 a in Embodiment 6, but the present invention isnot limited to this. The impurity element which imparts n-typeconductivity may also be added in the step of FIG. 15A, and then themasks 409 a to 412 a may be removed.

A mask 433 is next formed on the semiconductor layer 404 so as to coverthe second conducting layers 421 a and 421 b. The mask 433 partiallyoverlaps with the second impurity region 431, sandwiching the gateinsulating film 406. A second doping process is then performed, and animpurity element which imparts n-type conductivity is added. Doping ofthe n-type conductivity imparting impurity element is performed atconditions in which the dosage is raised higher than that of the firstdoping process, and at a low acceleration voltage. (See FIG. 15B). Thedoping can be carried out by ion doping or ion implantation. Ion dopingis performed under conditions of a dose amount from 1×10¹³ to 5×10¹⁴atoms/cm² and an acceleration voltage of 60 to 100 keV. A periodic tablegroup 15 element, typically phosphorous (P) or arsenic (As) is used asthe impurity element which imparts n-type conductivity, and phosphorous(P) is used here. The second conducting layers 419 to 422 become maskswith respect to the n-type conductivity imparting impurity element inthis case, and source regions 434 to 437, drain regions 438 to 441, andLov regions 442 to 445 are formed in a self-aligning manner. Further,Loff region 446 is formed in accordance with the mask 433. The impurityelement which imparts n-type conductivity is added to the source regions434 to 437, and to the drain regions 438 to 441 with a concentration inthe range of 1×10²⁰ to 1×10²¹ atoms/cm³.

It is possible to freely set the length of the Loff region 446 bycontrolling the size of the mask 433 according to Embodiment 6.

Note that in the specification, the LDD region overlapping with a gateelectrode through a gate insulating film is referred to as an Lovregion, and the LDD region not overlapping with a gate electrode througha gate insulating film is referred to as an Loff region.

The impurity element which imparts n-type conductivity is added at aconcentration of 1×10¹⁷ to 1×10¹⁹ atoms/cm³ in the Loff region, and at aconcentration of 1×10¹⁶ to 1×10¹⁸ atoms/cm³ in the Lov region.

Note that, in FIG. 15B, either before or after doping of an impurityelement which imparts n-type conductivity is performed at the abovestated conditions, doping of an n-type conductivity imparting impurityelement may also be performed with an acceleration voltage of 70 to 120keV in a state in which the mask 433 is formed on the semiconductorlayer 404. The concentration of the n-type conductivity impartingimpurity element in a portion 446 which becomes an Loff region of theswitching TFT can be suppressed in accordance with the above process,and the concentration of the n-type conductivity imparting impurityelement in portions 442 and 443, which become Lov regions of the TFTsused in the driver circuit can be increased. It is possible to lower theoff current of the switching TFT by suppressing the concentration of then-type conductivity imparting impurity element in the portion 446 whichbecomes the Loff region of the switching TFT. Further, hot carriersgenerated in accordance with a high electric field in the vicinity ofthe drain and a cause of a degradation phenomenon due to the hot carriereffect can be prevented by increasing the concentration of the n-typeconductivity imparting impurity element in the portion 443 which becomesthe Lov region of the n-channel TFT used in the driver circuit.

After removing the mask 433, source regions 447 and 448, drain regions449 and 450, and Lov regions 451 and 452, into which an impurity elementhaving a conductivity type which is the inverse of the above oneconductivity type, are then formed in the semiconductor layers 402 and405 for forming the p-channel TFT, as shown in FIG. 15C. The secondshape conducting layers 419 and 422 are used as a mask with respect tothe impurity element, and the impurity regions are formed in aself-aligning manner. The semiconductor layers 403 and 404, which formn-channel TFTs, are covered over their entire surface areas by a resistmasks 453 at this point. Phosphorous is added in differing concentrationto the source regions 447 and 448, the drain regions 449 and 450, andthe Lov regions 451 and 452, and ion doping is performed here usingdiborane (B₂H₆), so that impurity is added to each of the regions with aconcentration of 2×10²⁰ to 2×10²¹ atoms/cm³.

Impurity regions (source regions, drain regions, Lov regions, and Loffregions) are formed in the respective semiconductor layers 402 to 405 bythe above processes. The second conducting layers 419 to 422 overlappingthe semiconductor layers function as gate electrodes.

A process of activating the impurity elements added to the respectivesemiconductor layers is then performed, with the aim of controllingconductivity type. Thermal annealing using an annealing furnace isperformed for this process. In addition, laser annealing and rapidthermal annealing (RTA) can also be applied. Thermal annealing isperformed with an oxygen concentration equal to or less than 1 ppm,preferably equal to or less than 0.1 ppm, in a nitrogen atmosphere at400 to 700° C., typically between 500 and 600° C. Heat treatment isperformed for 4 hours at 500° C. in Embodiment 6. However, for cases inwhich the wiring material used in the conducting layers 419 to 422 isweak with respect to heat, it is preferable to perform activation afterforming an interlayer insulating film (having silicon as its mainconstituent) in order to protect the wirings and the like.

In addition, heat treatment is performed for 1 to 12 hours at 300 to450° C. in an atmosphere containing between 3 and 100% hydrogen,performing hydrogenation of the semiconductor layers. This process isone of terminating dangling bonds in the semiconductor layers byhydrogen which is thermally excited. Plasma hydrogenation (usinghydrogen excited by a plasma) may also be performed as another means ofhydrogenation.

A first interlayer insulating film 455 is formed next from a siliconnitride oxide film having a thickness of 100 to 200 nm. (FIG. 16A) Asecond interlayer insulating film 458 made from an organic insulatingmaterial is then formed on the first interlayer insulating film 455.

Contact holes are then formed in the gate insulating film 406, the firstinterlayer insulating film 455 and the second interlayer insulating film458, and source wirings 459 to 462 are formed to contact the sourceregions 447, 435, 436, and 448 through the contact holes. In the sameway, drain wirings 463 to 465 are further formed to contact the drainregions 449, 439, 440 and 450. (FIG. 16B)

Note that it is preferable to form the contact holes by dry etchingusing CF₄ and O₂ when the gate insulating film 406, the first interlayerinsulating film 455, and the second interlayer insulating film 458 areSiO₂ films or SiON films. Further, for cases in which the gateinsulating film 406, the first interlayer insulating film 455, and thesecond interlayer insulating film 458 are organic resin films, it ispreferable to form the contact holes by dry etching using CHF³ or by BHF(buffered hydrogen fluoride, HF+NH₄F). In addition, if the gateinsulating film 406, the first interlayer insulating film 455 and thesecond interlayer insulating film 458 are formed by different materials,it is preferable to change the method of etching and the etchant oretching gas type for each film. The contact holes may also be formed byusing the same etching method and the same etchant or etching gas.

A third interlayer insulating film 467 is formed next from an organicresin. Organic resins such as polyimide, polyamide, acrylic, and BCB(benzocyclobutene) can be used. In particular, it is preferable to useacrylic, which has superior levelness, because the third interlayerinsulating film 467 is formed with a strong implication of leveling. Anacrylic film is formed in Embodiment 6 at a film thickness at whichsteps formed by the TFTs can be sufficiently leveled. The film thicknessis preferably from 1 to 5 μm (more preferably between 2 and 4 μm).

A contact hole for reaching the drain wiring 465 is formed next in thethird interlayer insulating film 467, and a pixel electrode 468 isformed. An indium oxide tin oxide (ITO) film is formed with a thicknessof 110 nm in Embodiment 6, and patterning is then performed, forming thepixel electrode 468. Further, a transparent conducting film in whichbetween 2 and 20% zinc oxide (ZnO) is mixed with indium oxide may alsobe used. The pixel electrode 468 becomes an anode of an EL element. (SeeFIG. 16C).

A first bank 469 and a second bank 470 are formed next from a resinmaterial. The first bank 469 and the second bank 470 are formed in orderto separate EL layers and cathodes, which are formed later, of adjacentpixels. It is therefore preferable that the second bank 470 stick outfarther horizontally than the first bank 469. Note that it is preferablethat the combined thickness of the first bank 469 and the second bank470 be made on the order of 1 to 2 μm, but there are no limitations onthis thickness provided that the EL layers and the cathodes formed laterof adjacent pixels can be separated. Further, it is necessary to formthe first bank 469 and the second bank 470 by an insulating film, and itis therefore possible to use materials such as an oxide or a resin, forexample. The first bank 469 and the second bank 470 may both be formedby the same material, and they may also be formed by differentmaterials. The first bank 469 and the second bank 470 are formed instripe shapes between pixels. The first bank 469 and the second bank 470may be formed on and along the source wirings (source signal lines), andmay be formed on and along the gate wirings (gate signal lines). Notethat the first bank 469 and the second bank 470 may also be formed by amaterial in which a pigment is mixed into a resin. (See FIG. 17A.)

An EL layer 471 and a cathode (MgAg electrode) 472 are formed next insuccession without exposure to the atmosphere using vacuum evaporation.Note that the film thickness of the EL layer 471 may be from 80 to 200nm (typically between 100 and 120 nm), and that the film thickness ofthe cathode 472 may be from 180 to 300 nm (typically between 200 and 250nm). Note also that, although only one pixel is shown in Embodiment 6,an EL layer which emits red color light, an EL layer which emits greencolor light, and an EL layer which emits blue color light are formed atthe same time at this point. Note that materials to form an EL layer anda cathode is partially laminated on the bank 470, however, in thisspecification, the materials are not included in the EL layer 471 andthe cathode 472.

The EL layers 471 are formed in order for a pixel corresponding to thecolor red, a pixel corresponding to the color green, and a pixelcorresponding to the color blue. However, the EL layers 471 lacksresistance with respect to solutions, and therefore each color must beformed separately without using a photolithography technique. It ispreferable to use a metal mask and cover the pixels other than thedesired pixel, and selectively form the EL layers 471 in only therequired locations.

Namely, first a mask is set so as to cover all of the pixels except forthose corresponding to the color red, and red color light-emitting ELlayers are selectively formed using the mask. Next, a mask is set so asto cover all of the pixels except for those corresponding to the colorgreen, and green color light-emitting EL layers are selectively formedusing the mask. Finally, a mask is set so as to cover all of the pixelsexcept for those corresponding to the color blue, and blue colorlight-emitting EL layers are selectively formed using the mask. Notethat, although the use of all different masks is described here, thesame mask may also be reused. Further, it is preferable to performprocessing until all pixel EL layers are formed without releasing thevacuum.

Note that a single layer structure composed of only a light-emittinglayer is shown in Embodiment 6 for the EL layer 471, but a structurehaving layers such as a hole transporting layer, a hole injecting layer,an electron transporting layer, and an electron injecting layer inaddition to the light-emitting layer may also be used for the EL layer.Various examples of these types of combinations have already beenreported, and all such structures may be used. A known material can beused as the EL layer 471. Considering the EL element driver voltage, itis preferable to use an organic material as the known material.

The cathode 472 is formed next. An example of using an MgAg electrode asthe cathode is shown in Embodiment 6, but it is also possible to useother known materials.

The TFT substrate having the structure as shown in FIG. 17B is thuscompleted. Note that, after forming the first bank 469 and the secondbank 470, it is effective to perform processing in succession withoutexposure to the atmosphere up through to the formation of the cathode472 by using a multi-chamber method (or an in-line method) thin filmformation apparatus.

In Embodiment 6, a source region 504, a drain region 505, an Loff region506, an Lov region 507, and a channel forming region 508 are containedin a semiconductor layer of a switching TFT 501. The Loff region 506 isformed so as not to overlap with the gate electrode 421 through the gateinsulating film 406. Further, the Lov region 507 is formed so as tooverlap with the gate electrode 421 through the gate insulating film406. This type of structure is extremely effective in reducing the offcurrent.

Further, a single gate structure is used as the switching TFT 501 inEmbodiment 6, but the present invention may also have a double gatestructure or another type of multi-gate structure for the switching TFT.Two TFTs are substantially connected in series by using the double gatestructure, giving the advantage of additionally reducing the offcurrent.

Further, the switching TFT 501 is an n-channel TFT in Embodiment 6, buta p-channel TFT may also be used.

A semiconductor layer of an EL driving TFT 502 contains a source region510, a drain region 511, an Lov region 512, and a channel forming region513. The Lov region 512 is formed so as to overlap with the gateelectrode 422 through the gate insulating film 406. Note that the ELdriving TFT 502 does not have the Loff region in Embodiment 6, but astructure having the Loff region may also be used.

Further, the EL driving TFT 502 is a p-channel TFT in Embodiment 6, butit may also be an n-channel TFT.

Note that the active matrix substrate of Embodiment 6 shows an extremelyhigh reliability, and its operational characteristics are alsoincreased, by arranging optimally structured TFT in not only the pixelportion, but also in the driver circuit portion.

First, a TFT having a structure in which hot carrier injection isreduced so as not to have a very large drop in operational speed is usedas an n-channel TFT 503 of a CMOS circuit forming the driver circuitportion. Note that circuits such as a shift register, a buffer, a levelshifter, and a sampling circuit (sample and hold circuits) are includedas the driver circuits here. Signal conversion circuits such as a D/Aconverter can also be included in the case of performing digital drive.

A semiconductor layer of the n-channel TFT 503 of the CMOS circuit inEmbodiment 6 contains a source region 521, a drain region 522, an Lovregion 523, and a channel forming region 524.

Further, it is not necessary to be concerned with the off current forthe n-channel TFT 203, and importance may be placed more on theoperation speed than the off current. The formation of the Lov region223 overlapping the gate electrode 120 through the gate insulating film106 is therefore effective in increasing the operating speed because theresistance components are reduced as much as possible.

Further, a semiconductor layer of a p-channel TFT 504 of the CMOScircuit contains a source region 531, a drain region 532, an Lov region533, and a channel forming region 534.

Note that, in practice, it is preferable to perform packaging (sealing)by a protecting film having high airtight characteristics and littleoutgassing (such as a laminate film or an ultraviolet hardened resinfilm) or by a transparent sealing material after completing up throughto the processes of FIG. 17B so as to have no exposure to theatmosphere. Further, if an inert gas is placed in the inside of thesealing material, and a drying agent (barium oxide, for example) isarranged on the inside of the sealing material, then the reliability ofthe EL element is increased.

Further, a connector (flexible printed circuit, FPC) is attached inorder to connect the elements formed on the substrate, with terminalsextended from the circuits, to external signal terminals afterincreasing the airtight characteristics in accordance with the packagingprocess or the like. A manufactured product is thus completed. This typeof deliverable state is referred to as an EL display device throughoutthis specification.

The widths of the gate electrodes in the direction of the channel lengthdiffer as stated above in accordance with manufacturing processes of thepresent invention. Therefore, it is possible to make the ionimplantation within the semiconductor layers arranged under the firstgate electrode less than the ion concentration within the semiconductorlayers not arranged under the first gate electrode by utilizing thedifference in ion penetration depth, due to the difference of gateelectrode thickness, when performing ion injection using the gateelectrodes as masks.

Further, in order to form the Loff regions using a mask, only the widthof Lov region needs to be controlled by etching. It becomes easy tocontrol positions of the Lov regions and the Loff regions.

Note that although an example in which light emitted from the EL layeris directed toward the substrate side is explained in Embodiment 6, thepresent invention is not limited to this, and a structure in which lightemitted from the EL layer is directed above the substrate may also beused. In this case, the cathode of the EL element becomes the pixelelectrode, and it is preferable that the EL driving TFT be an n-channelTFT.

The method of manufacturing an EL display device of the presentinvention is not limited to the manufacturing method described inEmbodiment 6, and other manufacturing methods can be utilized.

Note that it is possible to freely combine Embodiment 6 with any ofEmbodiments 1 to 5.

Embodiment 7

An example in which a portable information terminal of the presentinvention has a touch panel is explained in Embodiment 7.

Reference numeral 1701 in FIG. 18A denotes a display portion of aportable information terminal of the present invention, referencenumeral 1702 denotes a touch panel, and reference numeral 1703 denotes atouch pen. The touch panel 1702 has light transmitting characteristics,and light emitted from the display portion 1701 and light irradiated tothe display portion 1701 can pass through the touch panel 1702. In acase an image is displayed on the display portion 1701 it is possiblefor an operator to see an image on the display portion 1701.

A detailed structure of the touch panel 1702 is shown in FIG. 18B. Aplurality of rectangular strip shape first resistive films 1704 alignedin a column direction, and a plurality of rectangular strip shape secondresistive films 1705 aligned in a row direction, are formed so as tooverlap while possessing a predetermined gap in the touch panel 1702.The first resistive films 1704 and the second resistive films 1705 areformed by ITO.

Differing voltages are applied to both ends of the first resistive films1704 aligned in the column direction, and a voltage gradient is formedin the column direction in portions within the first resistive films1704. Differing voltages are also applied to both ends of the secondresistive films 1705 aligned in the row direction, and a voltagegradient is formed in the row direction in portions within the secondresistive films 1705.

By applying a pressure on the surface of the touch panel 1702 by using ameans such as the touch pen, one of the first resistive films 1704 andone of the second resistive films 1705 are contacted. A voltage isgenerated corresponding to the position contacted, and by measuring thevoltage, information on the position of the first resistive films 1704and the second resistive films 1705 contacted can be written in to theportable information terminal as electronic data.

The portable information terminal of the present invention can displayan image written in to the display portion 1701 and can write in a takenin image by the touch pen 1703 with the above structure.

Note that it is possible to freely combine Embodiment 7 with any ofEmbodiments 1 to 6.

Embodiment 8

An example in which a display portion of a portable information terminalof the present invention functions as an area sensor is explained inEmbodiment 8. A structure of the display portion of Embodiment 8 isexplained in detail below. FIG. 19 shows a circuit diagram of a displayportion of this embodiment.

Source signal lines S1 to Sx, electric power source supply lines V1 toVx, gate signal lines G1 to Gy, reset gate signal lines RG1 to RGy,sensor gate signal lines SG1 to SGy, sensor output wirings SS1 to SSx,and a sensor electric power source line VB are formed in a displayportion 901.

The display portion 901 has a plurality of pixels 902. The pixels 902have one of the source signal lines S1 to Sx, one of the electric powersource supply lines V1 to Vx, one of the gate signal lines G1 to Gy, oneof the reset gate signal lines RG1 to RGy, one of the sensor gate signallines SG1 to SGy, one of the sensor output wirings SS1 to SSx, and thesensor electric power source line VB.

The sensor output wirings SS1 to SSx are connected to constant electriccurrent power supplies 903_1 to 903 _(—) x, respectively.

A detailed structure of the pixel 902 is shown in FIG. 20. A regionenclosed by a dotted line is the pixel 902. Note that a source signalline S denotes one of the source signal lines S1 to Sx. Further, anelectric power source supply line V denotes one of the electric powersource supply lines V1 to Vx. A gate signal line G denotes one of thegate signal lines G1 to Gy, and a reset gate signal line RG denotes oneof the reset gate signal lines RG1 to RGy. In addition, a sensor gatesignal line SG denotes one of the sensor gate signal lines SG1 to SGy,and a sensor output wiring SS denotes one of the sensor output wiringsSS1 to SSx.

The pixel 902 has a switching TFT 904, an EL driver TFT 905, and an ELelement 906. Further, in FIG. 20 a capacitor 907 is formed in the pixel902, but the capacitor 907 need not be formed.

A gate electrode of the switching TFT 904 is connected to the gatesignal line G. One of a source region and a drain region of theswitching TFT 904 is connected to the source signal line S, and theother is connected to a gate electrode of the EL driver TFT 905.

The source region of the EL driver TFT 905 is connected to the electricpower source supply line V, and the drain region of the EL driver TFT905 is connected to the EL element 906. The capacitor 907 is formedconnected to the gate electrode of the EL driver TFT 905 and to theelectric power source supply line V.

The EL element 906 is composed of an anode, a cathode, and an EL layerformed between the anode and the cathode. When the anode is connected toa drain region of the EL driver TFT 905, the anode becomes a pixelelectrode and the cathode becomes an opposing electrode. Conversely,when the cathode is connected to a drain region of the EL driver TFT905, the anode becomes the opposing electrode and the cathode becomesthe pixel electrode.

In addition, the pixel 902 has a reset TFT 910, a buffer TFT 911, aselection TFT 912, and a photodiode 913.

A gate electrode of the reset TFT 910 is connected to the reset gatesignal line RG. A source region of the reset TFT 910 is connected to thesensor electric power source line VB, and the sensor electric powersource line VB is always maintained at a constant electric potential(standard electric potential). Further, a drain region of the reset TFT910 is connected to the photodiode 913 and to a gate electrode of thebuffer TFT 911.

Although not shown in the figure, the photodiode 913 has a cathode, ananode, and a photoelectric conversion layer formed between the cathodeelectrode and the anode electrode. The drain region of the reset TFT 910is connected specifically to the anode electrode or the cathodeelectrode of the photodiode 913.

A drain region of the buffer TFT 911 is connected to the sensor electricpower source line VB, and is always maintained at the standard electricpotential. A source region of the buffer TFT 911 is connected to asource region or a drain region of the selection TFT 912.

A gate electrode of the selection TFT 912 is connected to the sensorgate signal line SG. One of a source region and a drain region of theselection TFT 912 is connected to the source region of the buffer TFT911, as stated above, and the other is connected to the sensor outputwiring SS. The sensor output wiring SS is connected to a constantelectric current power source 903 (one of the constant electric currentpower sources 903_1 to 903 _(—) x), and a constant electric alwaysflows.

An explanation of a method of driving the display portion of Embodiment8 is explained next using FIGS. 19 and 20.

The EL element 906 of the pixel 902 functions as a light source of thearea sensor, and the switching TFT 904 and the EL driver TFT 905 controlthe operation of the EL element 906 as the light source.

Light emitted from the EL element is reflected by the subject and isirradiated to the photodiode 913 of the pixel 902. The photodiode 913converts the irradiated light to an electrical signal having imageinformation. The electrical signal having image information which isgenerated by the photodiode 913 is then taken in within the portableinformation terminal as an image signal by the buffer TFT 911 and theselection TFT 912.

The reset TFT 910, the buffer TFT 911, and the selection TFT 912 may beeither an n-channel TFT or a p-channel TFT in Embodiment 8. However, itis preferable that the reset TFT 910 and the buffer TFT 911 haveopposite polarities.

First, the reset TFTs 910 of a first line of pixels connected to thereset gate signal line RG1 are placed in an ON state in accordance witha reset signal input to the reset gate signal line RG1. The standardelectric potential of the sensor electric power source line VB istherefore applied to the gate electrode of the buffer TFT 911.

Further, the selection TFTs 912 of a first line of pixels connected tothe sensor gate signal line SG1 are placed in an OFF state in accordancewith a sensor signal input to the sensor gate signal line SG1. Thesource region of the buffer TFT 911 is therefore maintained at anelectric potential in which an electric potential difference V_(GS)between the source region and the gate electrode of the buffer TFT 911is subtracted from the standard electric potential. Note that a periodduring which the reset TFT 910 is in an ON state is referred to as areset period in this embodiment.

The electric potential of the reset signal input to the reset gatesignal line RG1 is then changed, and all of the reset TFTs 910 of thefirst line of pixels are placed in an OFF state. The standard electricpotential of the sensor electric power source line VB is therefore nolonger applied to the gate electrodes of the buffer TFTs 911 of thefirst line of pixels. Note that a period during which the reset TFT 910is in an OFF state is referred to as a sample period ST in thisembodiment. In particular, a period during which the reset TFTs 910 ofthe first line of pixels is in an OFF state is referred to as a sampleperiod ST1.

The electric potential of the sensor signal input to the sensor gatesignal line SG1 changes in the sample period ST1, and the selection TFTs912 of the first line of pixels are placed in an ON state. The sourceregions of the buffer TFTs 911 of the first line of pixels are thereforeelectrically connected to the sensor output wiring SS1, through theselection TFTs 912. The sensor output wiring SS1 is connected to theconstant electric current power source 903_1, and therefore the bufferTFTs 911 function as source followers, and the electric potentialdifference V_(GS) between the source region and the gate electrode isconstant.

An electric current flows in the photodiode 913 in the sample period ST1when light from the EL element 906 is reflected by a subject and isirradiated to the photodiode 913. The electric potential of the gateelectrode of the buffer TFT 911, maintained at the standard electricpotential during the reset period, therefore changes in correspondencewith the amount of electric current which develops in the photodiode913.

The electric current flowing in the photodiode 913 is proportional tothe strength of the light irradiated to the photodiode 913, andtherefore the image of the subject is converted as is in the photodiode913 into an electrical signal. The electrical signal generated in thephotodiode 913 is input to the gate electrode of the buffer TFT 911.

The electric potential difference V_(GS) between the source region andthe gate electrode of the buffer TFT 911 is always constant, andtherefore the source region of the buffer TFT 911 maintains an electricpotential in which V_(GS) is subtracted from the electric potential ofthe gate electrode of the buffer TFT 911. Therefore, if the electricpotential of the gate electrode of the buffer TFT 911 changes, theelectric potential of the source region of the buffer TFT 911 alsochanges in accompaniment.

The electric potential of the source region of the buffer TFT 911 isinput to the sensor output wiring SS1, through the selection TFT 912, asan image signal.

Next, the reset TFTs 910 of the first line of pixels connected to thereset gate signal line RG1 are placed in an ON state in accordance withthe reset signal input to the reset gate signal line RG1, and the resetperiod again begins. The reset TFTs 910 of a second line of pixelsconnected to the reset gate signal line RG2 are also simultaneouslyplaced in an ON state in accordance with the reset signal input to thereset gate signal line RG2, and a sampling period ST2 begins.

An electrical signal having image information is generated in thephotodiode in the sampling period ST2, similar to what occurs in thesampling period ST1, and the image signal is input to the sensor outputwiring SS2.

If the above operations are repeated, one image can be read in as animage signal when the sampling period STy is complete. Note that aperiod up through the appearance of all of the sampling periods ST1 toSTy is referred to as a sensor frame period SF in this specification.

Further, it is necessary to always emit light from the EL elements ofeach pixel in each sampling period. For example, it is at leastnecessary for the EL elements of the first line of pixels to emit lightduring the sampling period ST1. Note that all of the pixels may alwaysemit light during the sensor frame SF.

Note also that for a case of an area sensor into which a color image iswritten, the display portion has pixels corresponding to each of thecolors R (red), G (green), and B (blue). The pixels corresponding toeach of the colors RGB have three types of EL elements corresponding toRGB, or have white color light emitting EL elements and three types ofcolor filters for RGB, or have blue color or blue-green color lightemitting EL elements and a fluorescing body (fluorescing colorconversion layer, CCM).

Each color of RGB light emitted from the pixels corresponding to each ofthe RGB colors is irradiated to the subject in order. Then each of theRGB colors of light reflected by the subject is irradiated to thephotodiodes of the pixels, and image signals corresponding to each ofthe RGB colors are taken in to the area sensor.

It is possible for the display portion to function as an area sensorwith the portable information terminal of Embodiment 8. It is thereforepossible to display an image, read in by the display portion, in thedisplay portion, to confirm the read in image on the spot, and it ispossible to send the image to another person as data.

Note that it is possible to freely combine Embodiment 8 with any ofEmbodiments 1 to 7.

An additionally detailed cross sectional structure of the displayportion is shown in FIG. 22 here, a top surface structure is shown inFIG. 23A and a circuit diagram is shown in FIG. 23B. FIGS. 22, 23A, and23B use common reference symbols and therefore may be mutuallyreferenced.

A switching TFT 4402 formed on a substrate 4401 in FIG. 22 is ann-channel TFT formed by using a known method. Further, a wiring denotedby reference numeral 4403 is a gate wiring electrically connected togate electrodes 4404 a and 4404 b of the switching TFT 4402.

Note that, although a double gate structure in which two channel formingregions are formed is used in Embodiment 9, a single gate structure inwhich one channel forming region is formed, and a triple gate structurein which three channel forming regions are formed, may also be used.

Further, a drain wiring 4405 of the switching TFT 4402 is electricallyconnected to a gate electrode 4407 of an EL driver TFT 4406. Note thatthe EL driver TFT 4406 is a p-channel TFT formed by using a knownmethod. Note also that, although a single gate structure is used inEmbodiment 9, a double gate structure and a triple gate structure mayalso be used.

A first passivation film 4408 is formed on the switching TFT 4402 and onthe EL driver TFT 4406, and a leveling film 4409 made from a resin isformed on the first passivation film. Leveling of steps due to the TFTsby using the leveling film 4409 is extremely important. An EL layersubsequently formed is extremely thin, and therefore light emissionirregularities may be caused by the existence of a step. It is thuspreferable to perform leveling before forming a pixel electrode so as tobe able to form the EL layer with a surface that is as level aspossible.

Furthermore, reference numeral 4410 denotes a pixel electrode (ELelement anode) made from a transparent conducting film, and the pixelelectrode is electrically connected to a drain wiring 4417 of the ELdriver TFT 4406. A chemical compound of indium oxide and tin oxide, achemical compound of indium oxide and zinc oxide, zinc oxide, tin oxide,and indium oxide can be used as the transparent conducting film.Further, a film in which gallium is added to the above films may also beused as a transparent conducting film.

An EL layer 4411 is formed on the pixel electrode 4410. Note that,although only one pixel is shown in FIG. 22, the EL layer is divided upand formed corresponding to the colors or R (red), G (green), and B(blue) in Embodiment 9. Further, a low molecular weight organic ELmaterial may be formed by an evaporation method in Embodiment 9.Specifically, a lamination structure may be formed in which a 20 nmthick copper phthalocyanine (CuPc) film is formed as a hole injectinglayer, and a 70 nm thick tris-8-aluminum quinolinolate complex (Alq₃)film may be formed on the CuPc film as a light emitting layer. The colorof light emitted can be controlled by adding a fluorescing pigment suchas quinacridon, perillin, and DCM1 to Alq₃.

Note that the above example is one example of organic EL materialscapable of being used as the EL layer, and the EL layer need not belimited to these. An EL layer in which a light emitting layer, a chargetransporting layer, and a charge injecting layer are freely combined(layers for emitting light and for performing transport of carriers forlight emission) may also be used. For example, an example of using lowmolecular weight organic EL materials as the EL layer is shown inEmbodiment 9, but high molecular weight EL materials may also be used.Further, it is also possible to use inorganic materials such as siliconcarbide as charge transporting layers and charge injecting layers. Knownmaterials can be used for these organic EL materials and inorganicmaterials.

A cathode 4412 made from a conducting film is formed next on the ELlayer 4411. An alloy film of aluminum and lithium is used as theconducting film in the case of Embodiment 9. Of course, a known MgAgfilm (an alloy film of magnesium and silver) may also be used. Aconducting film made from an element residing in group 1 or group 2 ofthe periodic table, or a conducting film to which one of the aboveelements is added, may be used as the cathode material.

An EL element 4413 is completed at the point where the cathode 4412 isformed. Note that the EL element 4413 indicates a capacitor formed bythe pixel electrode (anode) 4410, the EL layer 4411, and the cathode4412 here.

A top surface structure of the pixel in Embodiment 9 is explained usingFIG. 23A. A source region of the switching TFT 4402 is connected to asource signal line 4415 containing a source wiring, and a drain regionof the switching TFT 4402 is connected to the drain wiring 4405.Further, the drain wiring 4405 is electrically connected to the gateelectrode 4407 of the EL driver TFT 4406. A source region of the ELdriver TFT 4406 is electrically connected to an electric power sourcesupply line 4416, and a drain region of the EL driver TFT 4406 iselectrically connected to a drain wiring 4417. Furthermore, the drainwiring 4417 is electrically connected to a pixel electrode (anode) 4418shown by a dotted line.

A storage capacitor is formed at this point in a region denoted byreference numeral 4419. The storage capacitor 4419 is formed in betweena semiconductor film 4420 electrically connected to the electric powersource supply line 4416, an insulating film (not shown in the figures)formed on the same layer as a gate insulating film, and the gateelectrode 4407. Furthermore, it is also possible to use a capacitanceformed by the gate electrode 4407, a layer (not shown in the figures)which is the same as a first interlayer insulating film, and theelectric power source supply line 4416 as a storage capacitor.

Embodiment 9

An example of fabricating an EL display device using the presentinvention will be explained in embodiment 9. Note that FIG. 21A is a topview of an EL display device using the present invention, and FIG. 21Bis a cross sectional view thereof.

In FIG. 21A and FIG. 21B, reference numeral 4001 denotes a substrate,4002 denotes a display portion, 4003 denotes a source side drivingcircuit, 4004 denotes a gate side driving circuit. The driving circuitsare connected to external equipment, through an FPC (flexible printedcircuit) 4006 via a wiring 4005.

At this time, a first sealing material 4101, a covering material 4102, afiller material 4103 and a second sealing material 4104 are provided soas to enclose the display portion 4002, source side driving circuit4003, and gate side driving circuit 4004.

A cross sectional diagram of FIG. 21A cut along the line A-A′ is shownin FIG. 21B. On the substrate 4001, a driver TFT 4201 included in thesource side driving circuit 4003 (an n-channel TFT and a p-channel TFTare shown here) and an EL driving TFT 4202 included in the pixel portion4002 (a TFT for controlling the current flowing to an EL element isshown here) are formed.

In this embodiment, a p-channel TFT and an n-channel TFT fabricated by aknown method are used for the driving TFT 4201 and a p-channel TFTfabricated by a known method used for an EL driving TFT 4202. Furtherthe display portion 4002 is provided the storage capacitor (not shown infigure) connected gate electrode of the EL driving TFT 4202.

An interlayer insulating film (leveling film) 4301 made from a resinmaterial is formed on the driver TFT 4201 and the pixel TFT 4202, and apixel electrode (anode) 4302 electrically connected to a drain of thepixel TFT 4202 thereon. The pixel electrode 4302 is formed from atransparent conductive film having large work function. As thetransparent conductive film, an indium oxide and tin oxide compound oran indium oxide and zinc oxide compound can be utilized. The transparentconductive film doped with gallium also can be used.

Then, an insulating film 4303 is formed on the pixel electrode 4302, andan opening portion is formed on the pixel electrode 4302. At the openingportion, an EL (electro-luminescence) layer 4304 is formed on the pixelelectrode 4302. A known organic EL material or inorganic EL material isused as the EL layer 4304. Both of low molecular type (monomer based)organic EL materials and high molecular type (polymer based) organic ELmaterials can be used as the organic materials.

A known evaporation of painting technique may be used to form the ELlayer 4304. The EL layer may have a lamination structure by freelycombining a hole injecting layer, a hole transporting layer, a lightemitting layer, an electron transporting layer, and an electroninjecting layer, or a single layer structure.

On the EL layer 4304, a cathode 4305 made of a conductive film having alight-shielding property (typically, a conductive film comprisingaluminum, copper, or silver as a main component, or a lamination film ofthose and other conductive film) is formed. It is preferable to removeas much as possible any moisture or oxygen existing in the interfacebetween the cathode 4305 and the EL layer 4304. It is thereforenecessary to use a method of depositing continuously the cathode 4305and the EL layer 4304 in vacuum or depositing the EL layer 4304 in anatmosphere of nitrogen or in a rare gas atmosphere, thereby a cathode4305 is formed without exposing to oxygen and moisture. The above filmdeposition becomes possible in embodiment 9 by using a multi-chambermethod (cluster tool method) film deposition apparatus.

Then, the cathode 4305 is electrically connected to the wiring 4005 inthe region denoted by reference numeral 4306. The wiring 4005 forimparting a predetermined voltage to the cathode 4305 is connected tothe FPC 4006 through an anisotropic conductive material 4307.

As mentioned above, an EL element is made from the pixel electrode(anode) 4302, the EL layer 4304 and the cathode 4305. The EL element isenclosed with a covering material 4102 which is laminated with thesubstrate 4001 through a first sealing material 4101 and a secondsealing material 4104, and sealed with a filer material 4103.

Materials such as a glass plate, a metal plate (typically, a stainlesssteel plate), a ceramic plate and a plastic material (including aplastic film) can be used as the covering material 4102. As plasticmaterial an FRP (fiberglass-reinforced plastic) plate, a PVF (polyvinylfluoride) film, a Mylar film, a polyester film, and an acrylic film canbe used. It is preferable to use a sheet structure in which aluminumfoil is sandwiched by a PVF film or a Mylar film.

Note that, for a case in which the emission direction of light emittedfrom the EL element is directed to the covering material side, it isnecessary for the covering material to possess transparency. In thecase, a transparent material such as a glass plate, a plastic plate, apolyester film or an acrylic film can be used.

Additionally, a filler material 4103 is formed using ultraviolet curingresin or thermally curable resin. PVC (polyvinyl chloride), acrylic,polyimide, epoxy resin, silicone resin, PVB (polyvinyl butyral), and EVA(ethylene vinyl acetate) can be used as the filler material. If a dryingagent (preferably, barium oxide) is formed on the inside of the fillermaterial 4103 or materials which can absorb oxygen, then it can suppressthe degradation of the EL element.

Further, spacer may be contained in the filler material 4103. At thistime, the spacer is formed by using barium oxide, thereby the spaceritself has a hygroscopic property. Further, in the case of providing thespacer, it is effective that a resin film is provided on the cathode4305 as a buffer layer for relaxation of pressure from the spacer.

Further, the wiring 4005 is electrically connected to the FPC 4006 viathe anisotropic conductive film 4307. The wiring 4005 transmits signalsforwarding the pixel portion 4002, source side driving circuit 4003 andgate side driving circuit 4004 to the FPC 4006 and are electricallyconnected to external equipment through the FPC 4006.

Also, in the present embodiment, a second sealing material 4104 isprovided to cover an exposure portion of the first sealing material 4101and portion of the FPC 4006 to obtain the structure in which the ELelement is completely shut out from the outside. In this way, the ELdisplay device has a cross sectional structure shown in FIG. 21B.

Embodiment 10

An EL display device having a pixel structure which differs from that ofEmbodiment 9 is explained in Embodiment 10. FIG. 24 is used in theexplanation. Note that the explanation of Embodiment 9 may be referredto regarding portions to which reference symbols identical to those ofFIG. 22 are attached.

An n-channel TFT is formed using a known method as an EL driver TFT 4501in FIG. 24. A gate electrode 4502 of the EL driver TFT 4501 is of courseelectrically connected to the drain wiring 4405 of the switching TFT4402. Further, a drain wiring 4503 of the EL driver TFT 4501 iselectrically connected to a pixel electrode 4504.

The pixel electrode 4504, composed of a conducting film, functions as acathode of an EL element in Embodiment 10. Specifically, an alloy filmof aluminum and lithium is used. However, a conducting film made from anelement residing in group 1 or group 2 of the periodic table, and aconducting film to which one of the above elements is added, may also beused.

An EL layer 4505 is formed on the pixel electrode 4504. Note that,although only one pixel is shown by FIG. 24, an EL layer correspondingto the color G (green) is formed in Embodiment 10 by an evaporationmethod or an application method (preferably spin coating). Specifically,a lamination structure is used, in which a 20 nm thick lithium fluoride(LiF) film is formed as an electron injecting layer, and a 70 nm thickPPV (polyparaphenylene vinylene) film is formed on the LiF film as alight emitting layer.

Next, an anode 4506 is formed on the EL layer 4505 from a transparentconducting film. A conducting film composed of a chemical compound ofindium oxide and tin oxide, or a chemical compound of indium oxide andzinc oxide, is used as the transparent conducting film in the case ofEmbodiment 10.

An EL element 4507 is completed at the point where the anode 4506 isformed. Note that the EL element 4507 referred to here indicates acapacitor formed by the pixel electrode (cathode) 4504, the EL layer4505, and the anode 4506.

For a case of a high voltage equal to or greater than 10 V applied tothe EL element, degradation due to the hot carrier effect in the ELdriver TFT 4501 appears. It is effective in this case to use ann-channel TFT, having a structure in which an LDD region 4509 of a drainregion side overlaps with the gate electrode 4502 through the gateinsulating film 4510, as the EL driver TFT 4501.

Further, the EL driver TFT 4501 of Embodiment 10 forms a parasiticcapacitance between the gate electrode 4502 and the LDD region 4509referred to as a gate capacitance. By regulating the gate capacitance,it can be made to possess a function similar to that of the storagecapacitor 4418 shown in FIGS. 23A and 23B. In particular, thecapacitance of the storage capacitor may be smaller for a case ofoperating the EL display device by a digital driving method than for acase of an analog driving method operation, and therefore the storagecapacitor can be substituted by the gate capacitance.

Note that for cases in which the voltage applied to the EL element is 10V or less, preferably equal to or less than 5 V, there is almost noproblem of degradation due to the above hot carrier effect, andtherefore an n-channel TFT having a structure in which the LDD region4509 is omitted may also be used in FIG. 24.

Embodiment 11

An EL display device of a display portion of a portable informationterminal of the present invention may also have a structure in whichseveral TFTs are formed within a pixel. For example, 4 to 6 or more TFTsmay be formed. It is possible to implement the present invention withoutplacing any limitations on the pixel structure of the EL display device.

Embodiment 12

An EL display device used in a display portion of a portable informationterminal of the present invention is not limited to an active matrixtype, and a passive type may also be used. A cross sectional diagram ofa display portion of an EL display device used in Embodiment 12 is shownin FIG. 26.

Anodes 2602 are formed having a rectangular strip shape in alignment ona substrate 2601. A matrix shape insulating film 2603 is formed on thesubstrate 2601 covering the anodes 2602. Banks 2604 are then formed onthe insulating film 2603 in order to separate adjacent EL layers andcathodes.

It is preferable to use a material having insulating characteristics toform the bank 2604 in order to also electrically separate the adjacentEL layers and cathodes.

EL layers 2605 and cathodes 2607 are then formed and laminated in orderon a passive substrate having the substrate 2601, the anodes 2602, theinsulating film 2603, and the banks 2604. The EL layers 2605 and thecathodes 2606 which are adjacent, sandwiching the banks 2604, areseparated by the banks 2604.

The passive type EL display device has an easier method of manufacture,and a lower cost, than the active matrix type EL display device. It istherefore possible to lower the cost of the portable informationterminal itself by using the passive type EL display device in thedisplay portion of the portable information terminal of the presentinvention.

Note that the passive type EL display device used in the display portionof the portable information terminal of the present invention is notlimited to the structure shown by Embodiment 12. A passive type ELdisplay device used in the display portion of the portable informationterminal of the present invention may have any type of structure.

It is possible to implement Embodiment 12 by freely combining it withEmbodiment 1 or Embodiment 7.

Embodiment 13

A structure of a liquid crystal display device of a display portion of aportable information terminal of the present invention is explained inEmbodiment 13. An example of a schematic diagram of the liquid crystaldisplay device of Embodiment 13 is shown in FIG. 27.

A source signal line driver circuit 1301 and a gate signal line drivercircuit 1302 are a portion of a driver circuit. Source signal lines 1303connected to the source signal line driver circuit 1301, and gate signallines 1304 connected to the gate signal line driver circuit 1302intersect in a display portion 1308. A pixel thin film transistor (pixelTFT) 1305, a liquid crystal cell 1306 in which a liquid crystal issandwiched between an opposing electrode and a pixel electrode, and astorage capacitor 1307 are formed in regions having the source signallines 1303 and the gate signal lines 1304.

An analog video signal (analog signal having image information) input tothe source signal lines 1303 is selected by the pixel TFTs 1305 andwritten into predetermined pixel electrodes.

The analog video signal, sampled by a timing signal output from thesource signal line driver circuit 1301, is supplied to the source signallines 1303.

Switching of corresponding pixel TFTs 1305 is performed in accordancewith a gate signal output from the gate side driver circuit 1302, andthe liquid crystal of the liquid crystal cells 1306 is driven inaccordance with the analog signal having image information output formthe source signal lines 1303. An image is thus displayed in the displayportion.

Note that the liquid crystal display device used in the display portionof the portable information terminal of the present invention is notlimited to the structure shown in Embodiment 13. The liquid crystaldisplay device used in the display portion of the portable informationterminal of the present invention may have any type of structure.

It is possible to implement Embodiment 13 by freely combining it withEmbodiment 1 or Embodiment 7.

Embodiment 14

EL for formation of an EL layer of an EL element, in an EL displaydevice of a display portion of a portable information terminal of thepresent invention, is explained.

It is possible to use all known materials for the EL used in the ELlayer of the EL element in the EL display device of the display portionof the portable information terminal of the present invention. However,it becomes possible to suppress the electric power consumption of theportable information terminal itself by using in particular materials inwhich the light emission efficiency is very high from among all known ELmaterials.

By utilizing the emission of light when returning to a base state from atriplet excitation state (phosphorescence), in addition to the emissionof light when returning to a base state from a singlet excitation state(fluorescence), the maximum external quantum efficiency can beincreased. Specifically, it is possible to increase the external quantumefficiency, approximately 5% for a case of only utilizing fluorescence,to approximately 10% or greater, typically up to 20%, for a case ofutilizing phosphorescence in addition to fluorescence. The maximum valueof the strength of emitted light can then be made equal to or greaterthan 251 m/W, typically approximately 401 m/W by utilizingphosphorescence in addition to fluorescence, compared to approximately201 m/W for a case of only utilizing fluorescence.

Materials such as the following can be given as EL materials capable ofutilizing phosphorescence in addition to fluorescence: PtOEP(2,3,7,8,12,13,17,18-octaethyl 21H, 23H-porphine platinum(II)); andIr(ppy)₃ (tris(2-phenylpyridine)iridium).

An EL element having an EL material with which phosphorescence is alsoutilized, in addition to fluorescence, has a higher light emissionefficiency when compared to an EL element having an EL material whichonly utilizes fluorescence, and the power consumption of the portableinformation terminal itself can thus be suppressed. The ease of use ofthe portable information terminal can therefore be made better bysuppressing the power consumption because the portable informationterminal is carried and used by an operator.

It is possible to implement Embodiment 14 by freely combining it withany of Embodiments 1 to 12.

Embodiment 15

A case of automatically switching the direction of images displayed in adisplay portion, or the direction of images such as characters,numerals, and symbols displayed in operation keys, in accordance with anangle θ between a display panel in a connection portion and an operationportion in a portable information terminal of the present invention, isexplained in detail in Embodiment 15.

A cross sectional diagram of a connection portion 801 of a portableinformation terminal of Embodiment 15 is shown in FIGS. 28A to 28C.Reference numeral 802 denotes a display panel, reference numeral 803denotes an operation panel, and both panels are connected in theconnection portion 801. Note that, although an example is shown inEmbodiment 15 in which reference numeral 802 denotes the display paneland reference numeral 803 denotes the operation panel, the presentinvention is not limited to this structure. Conversely, referencenumeral 802 may also denote the operation panel and reference numeral803 may also denote the display panel.

The display panel 802 is connected to a rotation shaft 804 in theconnection portion 801. A cross section of the rotation shaft 804 has ashape in which a portion of a circle has been removed. This becomes anarc shape in Embodiment 15.

Further, the operation panel 803 is connected to a rotation portion 805in the connection portion 801. It is possible to perform rotation in therotation portion 805 with the rotation shaft 804 as a main axis, and theangle θ between the display panel 802 and the operation panel 803 isdetermined in accordance with the angle of rotation of the rotationportion 805.

A button 806 is formed in the rotation portion 805 in order to recognizethe angle θ between the display panel 802 and the operation panel 803.It is possible to sense the angle θ by whether or not the button 806contacts a portion of the arc or the rotation shaft 804.

Cross sectional diagrams of the connection portion 801 for cases inwhich θ=0°, θ=30°, and θ=120° are shown in FIGS. 28A, 28B, and 28C,respectively.

For example, the rotation shaft 804 contacts the button 806 when θ=0° inFIG. 28A and when θ=30° in FIG. 28B. The rotation shaft 804 is separatedfrom the button 806 for the case of θ=120° in FIG. 28C.

The direction of the image displayed in the display portion, and thedirection of the images such as characters, numerals, and symbolsdisplayed in the operation keys, switch depending upon whether or notthe button 806 contacts the rotation shaft 804. It is possible toautomatically switch the direction of the image displayed in the displayportion, and the direction of the images such as characters, numerals,and symbols displayed in the operation keys, in accordance with theangle θ formed between the display panel and the operation panel in theconnection portion in accordance with the above structure.

Note that it is possible for a designer to suitably determine thespecific value of the angle θ at which the image direction is switchedby changing the shape of the rotation shaft 804.

It is possible to implement Embodiment 15 by freely combining it withany of Embodiments 1 to 14.

A portable information terminal of the present invention has operationkeys for inputting characters, symbols, numerals and the like, each withan LED (light emitting diode), an EL display device, or a liquid crystaldisplay device and the like, and by displaying characters, symbols, andnumerals in the operation keys in accordance with the LEDs (lightemitting diodes), EL display devices, or liquid crystal display devices,an operator can differentiate between the operation keys. The operatorcan even discern the operation keys in a dark environment in accordancewith the above structure.

The operator can appropriately change the direction of the display ofthe EL display device used in the display portion, and can appropriatelychange the direction of the images such as characters, symbols, andnumerals displayed in the operation keys, in accordance with theportable information terminal usage. The ease of use of the portableinformation terminal can be increased with the above structure.

Further, the portable information terminal of the present invention mayalso use a structure having a CCD camera. By using the CCD camera, theoperator can send image information, taken in as electronic data to theportable image terminal by the CCD camera, to other persons on the spot.

What is claimed:
 1. An electronic device comprising: a first pluralityof pixels displaying an image; a second plurality of pixels displayingan operation key; and a touch panel provided adjacent to the firstplurality of pixels, wherein each of the first plurality of pixelscomprises: a first thin film transistor comprising a first gateelectrically connected to a first gate signal line, a first source and afirst drain; a second thin film transistor comprising a second gateelectrically connected to a second gate signal line, one of a secondsource and a second drain electrically connected to one of the firstsource and the first drain, and the other one of the second source andthe second drain electrically connected to a third line; a third thinfilm transistor comprising a third gate electrically connected to one ofthe first source and the first drain and one of the second source andthe second drain, a third source and a third drain; and a light emittingelement electrically connected to one of the third source and the thirddrain, and wherein each of directions of the image and the operation keyis switchable between a first orientation and a second orientation. 2.An electronic device comprising: a first plurality of pixels displayingan image; a second plurality of pixels displaying an operation key; atouch panel provided adjacent to the first plurality of pixels, andcomprising: a first plurality of strip shape films; and a secondplurality of strip shape films provided over and crossing the firstplurality of strip shape films; an audio input portion; and an audiooutput portion; wherein each of the first plurality of pixels comprises:a first thin film transistor comprising a first gate electricallyconnected to a first gate signal line, a first source and a first drain;a second thin film transistor comprising a second gate electricallyconnected to a second gate signal line, one of a second source and asecond drain electrically connected to one of the first source and thefirst drain, and the other one of the second source and the second drainelectrically connected to a third line; a third thin film transistorcomprising a third gate electrically connected to one of the firstsource and the first drain and one of the second source and the seconddrain, a third source and a third drain; and a light emitting elementelectrically connected to one of the third source and the third drain,and wherein each of directions of the image and the operation key isswitchable between a first orientation and a second orientation.
 3. Anelectronic device comprising: a first plurality of pixels displaying animage; a second plurality of pixels displaying an operation key; a touchpanel provided adjacent to the first plurality of pixels, andcomprising: a first plurality of strip shape films; and a secondplurality of strip shape films provided over and crossing the firstplurality of strip shape films; a CCD light receiving portion, whereineach of the first plurality of pixels comprises: a first thin filmtransistor comprising a first gate electrically connected to a firstgate signal line, a first source and a first drain; a second thin filmtransistor comprising a second gate electrically connected to a secondgate signal line, one of a second source and a second drain electricallyconnected to one of the first source and the first drain, and the otherone of the second source and the second drain electrically connected toa third line; a third thin film transistor comprising a third gateelectrically connected to one of the first source and the first drainand one of the second source and the second drain, a third source and athird drain; and a light emitting element electrically connected to oneof the third source and the third drain, and wherein each of directionsof the image and the operation key is switchable between a firstorientation and a second orientation.
 4. An electronic devicecomprising: a first plurality of pixels displaying an image; a secondplurality of pixels displaying an operation key; a touch panel providedadjacent to the first plurality of pixels, and comprising: a firstplurality of strip shape films; and a second plurality of strip shapefilms provided over and crossing the first plurality of strip shapefilms; wherein each of the first plurality of pixels comprises: a firstthin film transistor comprising a first gate electrically connected to afirst gate signal line, a first source and a first drain; a second thinfilm transistor comprising a second gate electrically connected to asecond gate signal line, one of a second source and a second drainelectrically connected to one of the first source and the first drain,and the other one of the second source and the second drain electricallyconnected to a third line; a third thin film transistor comprising athird gate electrically connected to one of the first source and thefirst drain and one of the second source and the second drain, a thirdsource and a third drain; and a light emitting element electricallyconnected to one of the third source and the third drain, and whereineach of directions of the image and the operation key is switchablebetween a first orientation and a second orientation.
 5. An electronicdevice according to claim 1, wherein the image is displayed an ELelement or liquid crystal.
 6. An electronic device according to claim 2,wherein the image is displayed an EL element or liquid crystal.
 7. Anelectronic device according to claim 3, wherein the image is displayedby an EL element or liquid crystal.
 8. An electronic device according toclaim 4, wherein the image is displayed an EL element or liquid crystal.9. An electronic device according to claim 1, wherein the operation keyis displayed by an EL element, liquid crystal or an LED.
 10. Anelectronic device according to claim 2, wherein the operation key isdisplayed by an EL element, liquid crystal or an LED.
 11. An electronicdevice according to claim 3, wherein the operation key is displayed byan EL element, liquid crystal or an LED.
 12. An electronic deviceaccording to claim 4, wherein the operation key is displayed by an ELelement, liquid crystal or an LED.
 13. An electronic device according toclaim 1, wherein the direction of the image and the direction of theoperation key is a same.
 14. An electronic device according to claim 2,wherein the direction of the image and the direction of the operationkey is a same.
 15. An electronic device according to claim 3, whereinthe direction of the image and the direction of the operation key is asame.
 16. An electronic device according to claim 4, wherein thedirection of the image and the direction of the operation key is a same.17. An electronic device according to claim 1, wherein the direction ofthe image and the direction of the operation key is different from eachother.
 18. An electronic device according to claim 2, wherein thedirection of the image and the direction of the operation key isdifferent from each other.
 19. An electronic device according to claim3, wherein the direction of the image and the direction of the operationkey is different from each other.
 20. An electronic device according toclaim 4, wherein the direction of the image and the direction of theoperation key is different from each other.
 21. An electronic deviceaccording to claim 1, wherein the touch panel has light transmittingcharacteristics.
 22. An electronic device according to claim 2, whereinthe touch panel has light transmitting characteristics.
 23. Anelectronic device according to claim 3, wherein the touch panel haslight transmitting characteristics.
 24. An electronic device accordingto claim 4, wherein the touch panel has light transmittingcharacteristics.
 25. An electronic device according to claim 2, whereineach of the first plurality of strip shape films and the secondplurality of strip shape films comprises ITO.
 26. An electronic deviceaccording to claim 3, wherein each of the first plurality of strip shapefilms and the second plurality of strip shape films comprises ITO. 27.An electronic device according to claim 4, wherein each of the firstplurality of strip shape films and the second plurality of strip shapefilms comprises ITO.
 28. An electronic device according to claim 1,wherein the first plurality of pixels are provided in a display panel,and the second plurality of pixels are provided in an operation panel.29. An electronic device according to claim 2, wherein the firstplurality of pixels are provided in a display panel, and the secondplurality of pixels are provided in an operation panel.
 30. Anelectronic device according to claim 3, wherein the first plurality ofpixels are provided in a display panel, and the second plurality ofpixels are provided in an operation panel.
 31. An electronic deviceaccording to claim 4, wherein the first plurality of pixels are providedin a display panel, and the second plurality of pixels are provided inan operation panel.
 32. An electronic device according to claim 1,wherein the third line is a power source supply line.
 33. An electronicdevice according to claim 2, wherein the third line is a power sourcesupply line.
 34. An electronic device according to claim 3, wherein thethird line is a power source supply line.
 35. An electronic deviceaccording to claim 4, wherein the third line is a power source supplyline.